diff --git a/composer.json b/composer.json
index 2f18026..7203d56 100644
--- a/composer.json
+++ b/composer.json
@@ -25,7 +25,7 @@
     }
   ],
   "require":     {
-    "php":      ">=8.0",
+    "php": "^8.1",
     "ext-curl": "*"
   },
   "autoload":    {
diff --git a/demos/domestic_rate.php b/demos/domestic_rate.php
index 367fa5d..b351671 100644
--- a/demos/domestic_rate.php
+++ b/demos/domestic_rate.php
@@ -2,6 +2,8 @@
 
 require_once('autoload.php');
 
+use USPS\Enum\MailType;
+use USPS\Enum\ServiceType;
 use USPS\RatePackage;
 
 // Initiate and set the username provided from usps
@@ -15,8 +17,8 @@
 // to set them as the example below
 // set the RatePackage for more info about the constants
 $package = (new RatePackage())
-    ->setService(RatePackage::SERVICE_FIRST_CLASS)
-    ->setFirstClassMailType(RatePackage::MAIL_TYPE_LETTER)
+    ->setService(ServiceType::FIRST_CLASS)
+    ->setFirstClassMailType(MailType::LETTER)
     ->setZipOrigination(91601)
     ->setZipDestination(91730)
     ->setPounds(0)
diff --git a/demos/open_label.php b/demos/open_label.php
index 6991c68..e6c41b5 100644
--- a/demos/open_label.php
+++ b/demos/open_label.php
@@ -3,13 +3,25 @@
 require_once('autoload.php');
 
 // Initiate and set the username provided from usps
-$label = new \USPS\OpenDistributeLabel('xxxx');
+$label = (new \USPS\OpenDistributeLabel('xxxx'))
+    ->setFromAddress(
+        'John',
+        'Doe',
+        '',
+        '5161 Lankershim Blvd',
+        'North Hollywood',
+        'CA',
+        '91601',
+        '# 204'
+    )->setToAddress(
+        'Vincent Gabriel',
+        '5440 Tujunga Ave',
+        'North Hollywood',
+        'CA',
+        '91601',
+        '707'
+    )->setWeightOunces(1);
 
-$label->setFromAddress('John', 'Doe', '', '5161 Lankershim Blvd', 'North Hollywood', 'CA', '91601', '# 204');
-$label->setToAddress('Vincent Gabriel', '5440 Tujunga Ave', 'North Hollywood', 'CA', '91601', '707');
-$label->setWeightOunces(1);
-
-// Perform the request and return result
 $label->createLabel();
 
 print_r($label->getPostData());
diff --git a/demos/priority_label.php b/demos/priority_label.php
index b393eb2..8a9989b 100644
--- a/demos/priority_label.php
+++ b/demos/priority_label.php
@@ -6,12 +6,28 @@
 $label = new \USPS\PriorityLabel('xxxx');
 
 // During test mode this seems not to always work as expected
-$label->setTestMode(true);
-
-$label->setFromAddress('John', 'Doe', '', '5161 Lankershim Blvd', 'North Hollywood', 'CA', '91601', '# 204', '', '8882721214');
-$label->setToAddress('Vincent', 'Gabriel', '', '230 Murray St', 'New York', 'NY', '10282');
-$label->setWeightOunces(1);
-$label->setField(36, 'LabelDate', '03/12/2014');
+$label->setTestMode(true)
+    ->setFromAddress(
+        'John',
+        'Doe',
+        '',
+        '5161 Lankershim Blvd',
+        'North Hollywood',
+        'CA',
+        '91601',
+        '# 204',
+        '',
+        '8882721214'
+    )->setToAddress(
+        'Vincent',
+        'Gabriel',
+        '',
+        '230 Murray St',
+        'New York',
+        'NY',
+        '10282'
+    )->setWeightOunces(1)
+    ->setField(36, 'LabelDate', '03/12/2014');
 
 // Perform the request and return result
 $label->createLabel();
diff --git a/src/Address.php b/src/Address.php
index c2fd0cd..21f9f78 100644
--- a/src/Address.php
+++ b/src/Address.php
@@ -18,16 +18,19 @@ class Address
     /**
      * Set the address2 property.
      *
-     * @param string|int $value
-     *
-     * @return Address
+     * @return $this
      */
-    public function setAddress(string|int $value): self
+    public function setAddress(string|int $value): static
     {
         return $this->setAddress2($value);
     }
 
-    public function setAddress2(string|int $value): self
+    /**
+     * Set the address2 property.
+     *
+     * @return $this
+     */
+    public function setAddress2(string|int $value): static
     {
         return $this->setField('Address2', $value);
     }
@@ -35,16 +38,14 @@ public function setAddress2(string|int $value): self
     /**
      * Set the address1 property usually the apt or suit number.
      *
-     * @param string|int $value
-     *
-     * @return Address
+     * @return $this
      */
-    public function setApt(string|int $value): self
+    public function setApt(string|int $value): static
     {
         return $this->setAddress1($value);
     }
 
-    public function setAddress1(string|int $value): self
+    public function setAddress1(string|int $value): static
     {
         return $this->setField('Address1', $value);
     }
@@ -52,11 +53,9 @@ public function setAddress1(string|int $value): self
     /**
      * Set the city property.
      *
-     * @param string|int $value
-     *
-     * @return Address
+     * @return $this
      */
-    public function setCity(string|int $value): self
+    public function setCity(string|int $value): static
     {
         return $this->setField('City', $value);
     }
@@ -64,11 +63,9 @@ public function setCity(string|int $value): self
     /**
      * Set the state property.
      *
-     * @param string|int $value
-     *
-     * @return Address
+     * @return $this
      */
-    public function setState(string|int $value): self
+    public function setState(string|int $value): static
     {
         return $this->setField('State', $value);
     }
@@ -76,11 +73,9 @@ public function setState(string|int $value): self
     /**
      * Set the zip4 property - zip code value represented by 4 integers.
      *
-     * @param string|int $value
-     *
-     * @return Address
+     * @return $this
      */
-    public function setZip4(string|int $value): self
+    public function setZip4(string|int $value): static
     {
         return $this->setField('Zip4', $value);
     }
@@ -88,28 +83,27 @@ public function setZip4(string|int $value): self
     /**
      * Set the zip5 property - zip code value represented by 5 integers.
      *
-     * @param string|int $value
-     *
-     * @return Address
+     * @return $this
      */
-    public function setZip5(string|int $value): self
+    public function setZip5(string|int $value): static
     {
         return $this->setField('Zip5', $value);
     }
 
-    public function setZipcode(string|int $value): self
+    /**
+     * @return $this
+     */
+    public function setZipcode(string|int $value): static
     {
         return $this->setZip5($value);
     }
 
     /**
-     * Set the firmname property.
+     * Set the firm name property.
      *
-     * @param string|int $value
-     *
-     * @return Address
+     * @return $this
      */
-    public function setFirmName(string|int $value): self
+    public function setFirmName(string|int $value): static
     {
         return $this->setField('FirmName', $value);
     }
@@ -117,12 +111,9 @@ public function setFirmName(string|int $value): self
     /**
      * Add an element to the stack.
      *
-     * @param string|int $key
-     * @param string|int $value
-     *
-     * @return Address
+     * @return $this
      */
-    public function setField(string|int $key, string|int $value): self
+    public function setField(string|int $key, string|int $value): static
     {
         $this->addressInfo[ucwords($key)] = $value;
 
@@ -131,8 +122,6 @@ public function setField(string|int $key, string|int $value): self
 
     /**
      * Returns a list of all the info we gathered so far in the current address object.
-     *
-     * @return array
      */
     public function getAddressInfo(): array
     {
diff --git a/src/AddressVerify.php b/src/AddressVerify.php
index 81b38d9..c16b7a6 100644
--- a/src/AddressVerify.php
+++ b/src/AddressVerify.php
@@ -25,8 +25,6 @@ class AddressVerify extends USPSBase
 
     /**
      * Perform the API call to verify the address.
-     *
-     * @return string
      */
     public function verify(): string
     {
@@ -35,8 +33,6 @@ public function verify(): string
 
     /**
      * returns array of all addresses added so far.
-     *
-     * @return array
      */
     public function getPostFields(): array
     {
@@ -47,10 +43,9 @@ public function getPostFields(): array
     /**
      * Add Address to the stack.
      *
-     * @param Address $data
-     * @param ?string  $id   the address unique id
+     * @return $this
      */
-    public function addAddress(Address $data, string $id = null): self
+    public function addAddress(Address $data, string $id = null): static
     {
         $packageId = $id !== null ? $id : ((count($this->addresses) + 1));
 
@@ -62,11 +57,9 @@ public function addAddress(Address $data, string $id = null): self
     /**
      * Set the revision value
      *
-     * @param string|int $value
-     *
-     * @return AddressVerify
+     * @return $this
      */
-    public function setRevision(string|int $value): self
+    public function setRevision(string|int $value): static
     {
         $this->revision = (string)$value;
 
diff --git a/src/CityStateLookup.php b/src/CityStateLookup.php
index 1f4dd31..81baf47 100644
--- a/src/CityStateLookup.php
+++ b/src/CityStateLookup.php
@@ -10,18 +10,16 @@
 class CityStateLookup extends USPSBase
 {
     /**
-     * @var string - the api version used for this type of call
+     * @var string the api version used for this type of call
      */
     protected string $apiVersion = 'CityStateLookup';
     /**
-     * @var array - list of all addresses added so far
+     * @var array list of all addresses added so far
      */
     protected array $addresses = [];
 
     /**
      * Perform the API call.
-     *
-     * @return string
      */
     public function lookup(): string
     {
@@ -30,8 +28,6 @@ public function lookup(): string
 
     /**
      * returns array of all addresses added so far.
-     *
-     * @return array
      */
     public function getPostFields(): array
     {
@@ -41,13 +37,9 @@ public function getPostFields(): array
     /**
      * Add zip zip code to the stack.
      *
-     * @param string $zip5 - zip code 5 integers
-     * @param string $zip4 - optional 4 integers zip code
-     * @param string $id   the address unique id
-     *
-     * @return void
+     * @return $this
      */
-    public function addZipCode($zip5, $zip4 = '', $id = null): void
+    public function addZipCode(string $zip5, string $zip4 = '', string $id = null): static
     {
         $packageId = $id !== null ? $id : ((count($this->addresses) + 1));
         $zipCodes = ['Zip5' => $zip5];
@@ -55,5 +47,7 @@ public function addZipCode($zip5, $zip4 = '', $id = null): void
             $zipCodes['Zip4'] = $zip4;
         }
         $this->addresses['ZipCode'][] = array_merge(['@attributes' => ['ID' => $packageId]], $zipCodes);
+
+        return $this;
     }
 }
diff --git a/src/Enum/MailType.php b/src/Enum/MailType.php
new file mode 100644
index 0000000..fb1a2ef
--- /dev/null
+++ b/src/Enum/MailType.php
@@ -0,0 +1,13 @@
+<?php declare(strict_types=1);
+
+namespace USPS\Enum;
+
+enum MailType: string
+{
+    case LETTER = 'LETTER';
+    case FLAT = 'FLAT';
+    case PARCEL = 'PARCEL';
+    case POSTCARD = 'POSTCARD';
+    case PACKAGE = 'PACKAGE';
+    case PACKAGE_SERVICE = 'PACKAGE SERVICE';
+}
\ No newline at end of file
diff --git a/src/Enum/ServiceType.php b/src/Enum/ServiceType.php
new file mode 100644
index 0000000..90e2ff5
--- /dev/null
+++ b/src/Enum/ServiceType.php
@@ -0,0 +1,24 @@
+<?php declare(strict_types=1);
+
+namespace USPS\Enum;
+
+enum ServiceType: string
+{
+    case FIRST_CLASS = 'FIRST CLASS';
+    case FIRST_CLASS_COMMERCIAL = 'FIRST CLASS COMMERCIAL';
+    case FIRST_CLASS_HFP_COMMERCIAL = 'FIRST CLASS HFP COMMERCIAL';
+    case PRIORITY = 'PRIORITY';
+    case PRIORITY_COMMERCIAL = 'PRIORITY COMMERCIAL';
+    case PRIORITY_HFP_COMMERCIAL = 'PRIORITY HFP COMMERCIAL';
+    case EXPRESS = 'EXPRESS';
+    case EXPRESS_COMMERCIAL = 'EXPRESS COMMERCIAL';
+    case EXPRESS_SH = 'EXPRESS SH';
+    case EXPRESS_SH_COMMERCIAL = 'EXPRESS SH COMMERCIAL';
+    case EXPRESS_HFP = 'EXPRESS HFP';
+    case EXPRESS_HFP_COMMERCIAL = 'EXPRESS HFP COMMERCIAL';
+    case PARCEL = 'PARCEL';
+    case MEDIA = 'MEDIA';
+    case LIBRARY = 'LIBRARY';
+    case ALL = 'ALL';
+    case ONLINE = 'ONLINE';
+}
\ No newline at end of file
diff --git a/src/FirstClassServiceStandards.php b/src/FirstClassServiceStandards.php
index f99a90b..d447fe0 100644
--- a/src/FirstClassServiceStandards.php
+++ b/src/FirstClassServiceStandards.php
@@ -8,18 +8,16 @@
 class FirstClassServiceStandards extends USPSBase
 {
     /**
-     * @var string - the api version used for this type of call
+     * @var string the api version used for this type of call
      */
     protected string $apiVersion = 'FirstClassMail';
     /**
-     * @var array - route added so far.
+     * @var array route added so far.
      */
     protected array $route = [];
 
     /**
      * Perform the API call.
-     *
-     * @return string
      */
     public function getServiceStandard(): string
     {
@@ -28,8 +26,6 @@ public function getServiceStandard(): string
 
     /**
      * returns array of all routes added so far.
-     *
-     * @return array
      */
     public function getPostFields(): array
     {
@@ -38,15 +34,14 @@ public function getPostFields(): array
 
     /**
      * Add route to the stack.
-     *
-     * @param $origin_zip
-     * @param $destination_zip
      */
-    public function addRoute($origin_zip, $destination_zip): void
+    public function addRoute(string|int $origin_zip, string|int $destination_zip): static
     {
         $this->route = [
             'OriginZip'      => $origin_zip,
             'DestinationZip' => $destination_zip,
         ];
+
+        return $this;
     }
 }
diff --git a/src/InternationalLabel.php b/src/InternationalLabel.php
index cd7182c..bcbde09 100644
--- a/src/InternationalLabel.php
+++ b/src/InternationalLabel.php
@@ -2,17 +2,14 @@
 
 namespace USPS;
 
-/**
- * Class InternationalLabel.
- */
 class InternationalLabel extends USPSBase
 {
     /**
-     * @var string - the api version used for this type of call
+     * @var string the api version used for this type of call
      */
     protected string $apiVersion = 'ExpressMailIntl';
     /**
-     * @var array - route added so far.
+     * @var array route added so far.
      */
     protected array $fields = [];
 
@@ -20,8 +17,6 @@ class InternationalLabel extends USPSBase
 
     /**
      * Perform the API call.
-     *
-     * @return string
      */
     public function createLabel(): string
     {
@@ -52,8 +47,6 @@ public function createLabel(): string
 
     /**
      * Return the USPS confirmation/tracking number if we have one.
-     *
-     * @return string|bool
      */
     public function getConfirmationNumber(): string|bool
     {
@@ -70,8 +63,6 @@ public function getConfirmationNumber(): string|bool
 
     /**
      * Return the USPS label as a base64 encoded string.
-     *
-     * @return string|bool
      */
     public function getLabelContents(): string|bool
     {
@@ -88,8 +79,6 @@ public function getLabelContents(): string|bool
 
     /**
      * returns array of all fields added.
-     *
-     * @return array
      */
     public function getPostFields(): array
     {
@@ -99,25 +88,17 @@ public function getPostFields(): array
     /**
      * Add shipping contents.
      *
-     * @param      $description
-     * @param      $value
-     * @param      $pounds
-     * @param      $ounces
-     * @param int $quantity
-     * @param null $tarrifNumber
-     * @param null $countryOfOrigin
-     *
-     * @return InternationalLabel
+     * @return $this
      */
     public function addContent(
-        $description,
-        $value,
-        $pounds,
-        $ounces,
+        string $description,
+        string $value,
+        string $pounds,
+        string $ounces,
         int $quantity = 1,
-        $tariffNumber = null,
-        $countryOfOrigin = null
-    ): self
+        string $tariffNumber = null,
+        string $countryOfOrigin = null
+    ): static
     {
         $this->contents['ItemDetail'][] = [
             'Description'     => $description,
@@ -135,19 +116,7 @@ public function addContent(
     /**
      * Set the from address.
      *
-     * @param string $firstName
-     * @param string $lastName
-     * @param string $company
-     * @param string $address
-     * @param string $city
-     * @param string $state
-     * @param string $zip
-     * @param string|null $address2
-     * @param string|null $zip4
-     * @param string|null $phone
-     * @param string|null $middleName
-     *
-     * @return InternationalLabel
+     * @return $this
      */
     public function setFromAddress(
         string $firstName,
@@ -161,7 +130,7 @@ public function setFromAddress(
         string $zip4 = null,
         string $phone = null,
         string $middleName = null
-    ): self
+    ): static
     {
         $this->setField(5, 'FromFirstName', $firstName);
         $this->setField(6, 'FromMiddleInitial', $middleName);
@@ -181,24 +150,7 @@ public function setFromAddress(
     /**
      * Set the to address.
      *
-     * @param string $firstName
-     * @param string $lastName
-     * @param string $company
-     * @param string $address
-     * @param string $city
-     * @param string $province
-     * @param string $country
-     * @param string $zip
-     * @param string|null $address2
-     * @param string $poBoxFlag
-     * @param string|null $phone
-     * @param string|null $fax
-     * @param string|null $email
-     *
-     * @return InternationalLabel
-     *
-     * @internal param string $state
-     * @internal param string $zip4
+     * @return $this
      */
     public function setToAddress(
         string $firstName,
@@ -214,7 +166,7 @@ public function setToAddress(
         string $phone = null,
         string $fax = null,
         string $email = null
-    ): self
+    ): static
     {
         $this->setField(16, 'ToFirstName', $firstName);
         $this->setField(17, 'ToLastName', $lastName);
@@ -237,13 +189,9 @@ public function setToAddress(
      * Set any other required string make sure you set the correct position as well
      * as the position of the items matters.
      *
-     * @param int    $position
-     * @param string $key
-     * @param mixed $value
-     *
-     * @return InternationalLabel
+     * @return $this
      */
-    public function setField(int $position, string $key, mixed $value): self
+    public function setField(int $position, string $key, mixed $value): static
     {
         $this->fields[$position.':'.$key] = $value;
 
@@ -255,9 +203,9 @@ public function setField(int $position, string $key, mixed $value): self
      *
      * @param float|int $weight
      *
-     * @return InternationalLabel
+     * @return $this
      */
-    public function setWeightOunces(float|int $weight): self
+    public function setWeightOunces(float|int $weight): static
     {
         $this->setField(33, 'GrossOunces', $weight);
 
@@ -269,9 +217,9 @@ public function setWeightOunces(float|int $weight): self
      *
      * @param float|int $weight
      *
-     * @return InternationalLabel
+     * @return $this
      */
-    public function setWeightPounds(float|int $weight): self
+    public function setWeightPounds(float|int $weight): static
     {
         $this->setField(32, 'GrossPounds', $weight);
 
diff --git a/src/OpenDistributeLabel.php b/src/OpenDistributeLabel.php
index 788a766..ca703ac 100644
--- a/src/OpenDistributeLabel.php
+++ b/src/OpenDistributeLabel.php
@@ -8,18 +8,16 @@
 class OpenDistributeLabel extends USPSBase
 {
     /**
-     * @var string - the api version used for this type of call
+     * @var string the api version used for this type of call
      */
     protected string $apiVersion = 'OpenDistributePriorityV2';
     /**
-     * @var array - route added so far.
+     * @var array route added so far.
      */
     protected array $fields = [];
 
     /**
      * Perform the API call.
-     *
-     * @return string
      */
     public function createLabel(): string
     {
@@ -45,10 +43,8 @@ public function createLabel(): string
 
     /**
      * Return the USPS confirmation/tracking number if we have one.
-     *
-     * @return string|bool
      */
-    public function getConfirmationNumber()
+    public function getConfirmationNumber(): string|bool
     {
         $response = $this->getArrayResponse();
         // Check to make sure we have it
@@ -63,10 +59,8 @@ public function getConfirmationNumber()
 
     /**
      * Return the USPS label as a base64 encoded string.
-     *
-     * @return string|bool
      */
-    public function getLabelContents()
+    public function getLabelContents(): string|bool
     {
         $response = $this->getArrayResponse();
 
@@ -82,10 +76,8 @@ public function getLabelContents()
 
     /**
      * returns array of all fields added.
-     *
-     * @return array
      */
-    public function getPostFields()
+    public function getPostFields(): array
     {
         return $this->fields;
     }
@@ -93,29 +85,20 @@ public function getPostFields()
     /**
      * Set the from address.
      *
-     * @param string $firstName
-     * @param string $lastName
-     * @param string $company
-     * @param string $address
-     * @param string $city
-     * @param string $state
-     * @param string $zip
-     * @param string $address2
-     * @param string $zip4
-     *
-     * @return object
+     * @return $this
      */
     public function setFromAddress(
-        $firstName,
-        $lastName,
-        $company,
-        $address,
-        $city,
-        $state,
-        $zip,
-        $address2 = null,
-        $zip4 = null
-    ) {
+        string $firstName,
+        string $lastName,
+        string $company,
+        string $address,
+        string $city,
+        string $state,
+        string $zip,
+        string $address2 = null,
+        string $zip4 = null
+    ): static
+    {
         $this->setField(5, 'FromName', trim($firstName.' '.$lastName));
         $this->setField(7, 'FromFirm', $company);
         $this->setField(8, 'FromAddress1', $address2);
@@ -131,17 +114,17 @@ public function setFromAddress(
     /**
      * Set the to address.
      *
-     * @param string $company
-     * @param string $address
-     * @param string $city
-     * @param string $state
-     * @param string $zip
-     * @param string $address2
-     * @param string $zip4
-     *
-     * @return object
+     * @return $this
      */
-    public function setToAddress($company, $address, $city, $state, $zip, $address2 = null, $zip4 = null)
+    public function setToAddress(
+        string $company,
+        string $address,
+        string $city,
+        string $state,
+        string $zip,
+        string $address2 = null,
+        string $zip4 = null
+    ): static
     {
         $this->setField(15, 'ToFacilityName', $company);
         $this->setField(18, 'ToFacilityAddress1', $address2);
@@ -157,11 +140,9 @@ public function setToAddress($company, $address, $city, $state, $zip, $address2
     /**
      * Set package weight in ounces.
      *
-     * @param $weight
-     *
      * @return $this
      */
-    public function setWeightOunces($weight)
+    public function setWeightOunces(int|string $weight): static
     {
         $this->setField(38, 'WeightInOunces', $weight);
 
@@ -171,11 +152,9 @@ public function setWeightOunces($weight)
     /**
      * Set package weight in ounces.
      *
-     * @param $weight
-     *
      * @return $this
      */
-    public function setWeightPounds($weight)
+    public function setWeightPounds(int|string $weight): static
     {
         $this->setField(37, 'WeightInPounds', $weight);
 
@@ -186,13 +165,9 @@ public function setWeightPounds($weight)
      * Set any other requried string make sure you set the correct position as well
      * as the position of the items matters.
      *
-     * @param int    $position
-     * @param string $key
-     * @param string $value
-     *
-     * @return object
+     * @return $this
      */
-    public function setField($position, $key, $value)
+    public function setField(int $position, string $key, string $value): static
     {
         $this->fields[$position.':'.$key] = $value;
 
@@ -201,10 +176,8 @@ public function setField($position, $key, $value)
 
     /**
      * Add missing required elements.
-     *
-     * @return void
      */
-    protected function addMissingRequired()
+    protected function addMissingRequired(): void
     {
         $required = [
             '1:Revision'                      => '',
diff --git a/src/PriorityLabel.php b/src/PriorityLabel.php
index 48f1aed..e320a35 100644
--- a/src/PriorityLabel.php
+++ b/src/PriorityLabel.php
@@ -8,18 +8,16 @@
 class PriorityLabel extends USPSBase
 {
     /**
-     * @var string - the api version used for this type of call
+     * @var string the api version used for this type of call
      */
     protected string $apiVersion = 'ExpressMailLabel';
     /**
-     * @var array - route added so far.
+     * @var array route added so far.
      */
     protected array $fields = [];
 
     /**
      * Perform the API call.
-     *
-     * @return string
      */
     public function createLabel(): string
     {
@@ -45,8 +43,6 @@ public function createLabel(): string
 
     /**
      * Return the USPS confirmation/tracking number if we have one.
-     *
-     * @return string|bool
      */
     public function getConfirmationNumber(): string|bool
     {
@@ -63,8 +59,6 @@ public function getConfirmationNumber(): string|bool
 
     /**
      * Return the USPS label as a base64 encoded string.
-     *
-     * @return string|bool
      */
     public function getLabelContents(): string|bool
     {
@@ -81,8 +75,6 @@ public function getLabelContents(): string|bool
 
     /**
      * Return the USPS receipt as a base64 encoded string.
-     *
-     * @return string|bool
      */
     public function getReceiptContents(): string|bool
     {
@@ -99,8 +91,6 @@ public function getReceiptContents(): string|bool
 
     /**
      * returns array of all fields added.
-     *
-     * @return array
      */
     public function getPostFields(): array
     {
@@ -110,31 +100,20 @@ public function getPostFields(): array
     /**
      * Set the from address.
      *
-     * @param string $firstName
-     * @param string $lastName
-     * @param string $company
-     * @param string $address
-     * @param string $city
-     * @param string $state
-     * @param string $zip
-     * @param string $address2
-     * @param string $zip4
-     * @param string $phone
-     *
-     * @return PriorityLabel
+     * @return $this
      */
     public function setFromAddress(
-        $firstName,
-        $lastName,
-        $company,
-        $address,
-        $city,
-        $state,
-        $zip,
-        $address2 = null,
-        $zip4 = null,
-        $phone = null
-    ): self
+        string $firstName,
+        string $lastName,
+        string $company,
+        string $address,
+        string $city,
+        string $state,
+        string $zip,
+        string $address2 = null,
+        string $zip4 = null,
+        string $phone = null
+    ): static
     {
         $this->setField(5, 'FromFirstName', $firstName);
         $this->setField(6, 'FromLastName', $lastName);
@@ -153,31 +132,20 @@ public function setFromAddress(
     /**
      * Set the to address.
      *
-     * @param string $firstName
-     * @param string $lastName
-     * @param string $company
-     * @param string $address
-     * @param string $city
-     * @param string $state
-     * @param string $zip
-     * @param string $address2
-     * @param string $zip4
-     * @param string $phone
-     *
-     * @return PriorityLabel
+     * @return $this
      */
     public function setToAddress(
-        $firstName,
-        $lastName,
-        $company,
-        $address,
-        $city,
-        $state,
-        $zip,
-        $address2 = null,
-        $zip4 = null,
-        $phone = null
-    ): self
+        string $firstName,
+        string $lastName,
+        string $company,
+        string $address,
+        string $city,
+        string $state,
+        string $zip,
+        string $address2 = null,
+        string $zip4 = null,
+        string $phone = null
+    ): static
     {
         $this->setField(15, 'ToFirstName', $firstName);
         $this->setField(16, 'ToLastName', $lastName);
@@ -196,11 +164,9 @@ public function setToAddress(
     /**
      * Set package weight in ounces.
      *
-     * @param $weight
-     *
-     * @return PriorityLabel
+     * @return $this
      */
-    public function setWeightOunces($weight): self
+    public function setWeightOunces(string $weight): static
     {
         $this->setField(25, 'WeightInOunces', $weight);
 
@@ -211,13 +177,9 @@ public function setWeightOunces($weight): self
      * Set any other requried string make sure you set the correct position as well
      * as the position of the items matters.
      *
-     * @param int    $position
-     * @param string $key
-     * @param string $value
-     *
-     * @return PriorityLabel
+     * @return $this
      */
-    public function setField($position, $key, $value): self
+    public function setField(int $position, string $key, string $value): static
     {
         $this->fields[$position.':'.$key] = $value;
 
@@ -226,8 +188,6 @@ public function setField($position, $key, $value): self
 
     /**
      * Add missing required elements.
-     *
-     * @return void
      */
     protected function addMissingRequired(): void
     {
diff --git a/src/Rate.php b/src/Rate.php
index bab2782..3a2424e 100644
--- a/src/Rate.php
+++ b/src/Rate.php
@@ -21,59 +21,49 @@ class Rate extends USPSBase
 
     /**
      * Perform the API call.
-     *
-     * @param int $timeout Time-out in seconds.
-     *
-     * @return string
      */
-    public function getRate($timeout = 60)
+    public function getRate(int $timeout = 60): string
     {
-        return $this->doRequest(NULL, $timeout);
+        return $this->doRequest(null, $timeout);
     }
 
     /**
      * returns array of all packages added so far.
-     *
-     * @return array
      */
-    public function getPostFields()
+    public function getPostFields(): array
     {
         return $this->packages;
     }
 
     /**
      * sets the type of call to perform domestic or international.
-     *
-     * @param $status
-     *
-     * @return array
      */
-    public function setInternationalCall($status)
+    public function setInternationalCall(bool $status): array
     {
         $this->apiVersion = $status === true ? 'IntlRateV2' : 'RateV4';
     }
 
     /**
      * Add other option for International & Insurance.
-     *
-     * @param string|int $key
-     * @param string|int $value
      */
-    public function addExtraOption($key, $value)
+    public function addExtraOption(string|int $key, mixed $value): static
     {
         $this->packages[$key][] = $value;
+
+        return $this;
     }
 
     /**
      * Add Package to the stack.
      *
-     * @param RatePackage $data
-     * @param string      $id   the address unique id
+     * @param string|null $id the address unique id
      */
-    public function addPackage(RatePackage $data, $id = null)
+    public function addPackage(RatePackage $data, string $id = null): static
     {
         $packageId = $id !== null ? $id : ((count($this->packages) + 1));
 
         $this->packages['Package'][] = array_merge(['@attributes' => ['ID' => $packageId]], $data->getPackageInfo());
+
+        return $this;
     }
 }
diff --git a/src/RatePackage.php b/src/RatePackage.php
index 3008ee8..d0b8526 100644
--- a/src/RatePackage.php
+++ b/src/RatePackage.php
@@ -2,6 +2,9 @@
 
 namespace USPS;
 
+use USPS\Enum\MailType;
+use USPS\Enum\ServiceType;
+
 /**
  * USPS Rate Package
  * used by the ups rate class to create packages represented as objects.
@@ -14,41 +17,16 @@ class RatePackage extends Rate
      * @var array - list of all packages added so far
      */
     protected array $packageInfo = [];
-    /**
-     * Services constants.
-     */
-    const SERVICE_FIRST_CLASS = 'FIRST CLASS';
-    const SERVICE_FIRST_CLASS_COMMERCIAL = 'FIRST CLASS COMMERCIAL';
-    const SERVICE_FIRST_CLASS_HFP_COMMERCIAL = 'FIRST CLASS HFP COMMERCIAL';
-    const SERVICE_PRIORITY = 'PRIORITY';
-    const SERVICE_PRIORITY_COMMERCIAL = 'PRIORITY COMMERCIAL';
-    const SERVICE_PRIORITY_HFP_COMMERCIAL = 'PRIORITY HFP COMMERCIAL';
-    const SERVICE_EXPRESS = 'EXPRESS';
-    const SERVICE_EXPRESS_COMMERCIAL = 'EXPRESS COMMERCIAL';
-    const SERVICE_EXPRESS_SH = 'EXPRESS SH';
-    const SERVICE_EXPRESS_SH_COMMERCIAL = 'EXPRESS SH COMMERCIAL';
-    const SERVICE_EXPRESS_HFP = 'EXPRESS HFP';
-    const SERVICE_EXPRESS_HFP_COMMERCIAL = 'EXPRESS HFP COMMERCIAL';
-    const SERVICE_PARCEL = 'PARCEL';
-    const SERVICE_MEDIA = 'MEDIA';
-    const SERVICE_LIBRARY = 'LIBRARY';
-    const SERVICE_ALL = 'ALL';
-    const SERVICE_ONLINE = 'ONLINE';
     /**
      * First class mail type
      * required when you use one of the first class services.
      */
-    const MAIL_TYPE_LETTER = 'LETTER';
-    const MAIL_TYPE_FLAT = 'FLAT';
-    const MAIL_TYPE_PARCEL = 'PARCEL';
-    const MAIL_TYPE_POSTCARD = 'POSTCARD';
-    const MAIL_TYPE_PACKAGE = 'PACKAGE';
-    const MAIL_TYPE_PACKAGE_SERVICE = 'PACKAGE SERVICE';
+
     /**
      * Container constants.
      */
-    const CONTAINER_VARIABLE = 'VARIABLE';
-    const CONTAINER_FLAT_RATE_ENVELOPE = 'FLAT RATE ENVELOPE';
+    public const CONTAINER_VARIABLE = 'VARIABLE';
+    public const CONTAINER_FLAT_RATE_ENVELOPE = 'FLAT RATE ENVELOPE';
     const CONTAINER_PADDED_FLAT_RATE_ENVELOPE = 'PADDED FLAT RATE ENVELOPE';
     const CONTAINER_LEGAL_FLAT_RATE_ENVELOPE = 'LEGAL FLAT RATE ENVELOPE';
     const CONTAINER_SM_FLAT_RATE_ENVELOPE = 'SM FLAT RATE ENVELOPE';
@@ -71,35 +49,29 @@ class RatePackage extends Rate
     /**
      * Set the service property.
      *
-     * @param string|int $value
-     *
-     * @return RatePackage
+     * @return $this
      */
-    public function setService(string|int $value): self
+    public function setService(ServiceType $value): static
     {
-        return $this->setField('Service', $value);
+        return $this->setField('Service', $value->value);
     }
 
     /**
      * Set the first class mail type property.
      *
-     * @param string|int $value
-     *
-     * @return RatePackage
+     * @return $this
      */
-    public function setFirstClassMailType(string|int $value): self
+    public function setFirstClassMailType(MailType $value): static
     {
-        return $this->setField('FirstClassMailType', $value);
+        return $this->setField('FirstClassMailType', $value->value);
     }
 
     /**
      * Set the zip origin property.
      *
-     * @param string|int $value
-     *
-     * @return RatePackage
+     * @return $this
      */
-    public function setZipOrigination(string|int $value): self
+    public function setZipOrigination(string|int $value): static
     {
         return $this->setField('ZipOrigination', $value);
     }
@@ -107,11 +79,9 @@ public function setZipOrigination(string|int $value): self
     /**
      * Set the zip destination property.
      *
-     * @param string|int $value
-     *
-     * @return RatePackage
+     * @return $this
      */
-    public function setZipDestination(string|int $value): self
+    public function setZipDestination(string|int $value): static
     {
         return $this->setField('ZipDestination', $value);
     }
@@ -119,11 +89,9 @@ public function setZipDestination(string|int $value): self
     /**
      * Set the pounds property.
      *
-     * @param string|int $value
-     *
-     * @return RatePackage
+     * @return $this
      */
-    public function setPounds(string|int $value): self
+    public function setPounds(string|int $value): static
     {
         return $this->setField('Pounds', $value);
     }
@@ -131,11 +99,9 @@ public function setPounds(string|int $value): self
     /**
      * Set the ounces property.
      *
-     * @param string|int $value
-     *
-     * @return RatePackage
+     * @return $this
      */
-    public function setOunces(string|int $value): self
+    public function setOunces(string|int $value): static
     {
         return $this->setField('Ounces', $value);
     }
@@ -143,11 +109,9 @@ public function setOunces(string|int $value): self
     /**
      * Set the container property.
      *
-     * @param string|int $value
-     *
-     * @return RatePackage
+     * @return $this
      */
-    public function setContainer(string|int $value): self
+    public function setContainer(string|int $value): static
     {
         return $this->setField('Container', $value);
     }
@@ -155,11 +119,9 @@ public function setContainer(string|int $value): self
     /**
      * Set the size property.
      *
-     * @param string|int $value
-     *
-     * @return RatePackage
+     * @return $this
      */
-    public function setSize(string|int $value): self
+    public function setSize(string|int $value): static
     {
         return $this->setField('Size', $value);
     }
@@ -167,12 +129,9 @@ public function setSize(string|int $value): self
     /**
      * Add an element to the stack.
      *
-     * @param string|int $key
-     * @param mixed $value
-     *
-     * @return RatePackage
+     * @return $this
      */
-    public function setField(string|int $key, mixed $value): self
+    public function setField(string|int $key, mixed $value): static
     {
         $this->packageInfo[ucwords($key)] = $value;
 
@@ -181,8 +140,6 @@ public function setField(string|int $key, mixed $value): self
 
     /**
      * Returns a list of all the info we gathered so far in the current package object.
-     *
-     * @return array
      */
     public function getPackageInfo(): array
     {
diff --git a/src/ServiceDeliveryCalculator.php b/src/ServiceDeliveryCalculator.php
index 656098b..e57dd33 100644
--- a/src/ServiceDeliveryCalculator.php
+++ b/src/ServiceDeliveryCalculator.php
@@ -8,18 +8,16 @@
 class ServiceDeliveryCalculator extends USPSBase
 {
     /**
-     * @var string - the api version used for this type of call
+     * @var string the api version used for this type of call
      */
     protected string $apiVersion = 'SDCGetLocations';
     /**
-     * @var array - route added so far.
+     * @var array route added so far.
      */
     protected array $route = [];
 
     /**
      * Perform the API call.
-     *
-     * @return string
      */
     public function getServiceDeliveryCalculation(): string
     {
@@ -28,8 +26,6 @@ public function getServiceDeliveryCalculation(): string
 
     /**
      * returns array of all routes added so far.
-     *
-     * @return array
      */
     public function getPostFields(): array
     {
@@ -37,7 +33,7 @@ public function getPostFields(): array
     }
 
     /**
-     * @param      $mail_class      integer from 0 to 6 indicating the class of mail.
+     * @param int $mailClass      integer from 0 to 6 indicating the class of mail.
      *                              “0” = All Mail Classes
      *                              “1” = Express Mail
      *                              “2” = Priority Mail
@@ -45,24 +41,31 @@ public function getPostFields(): array
      *                              “4” = Standard Mail
      *                              “5” = Periodicals
      *                              “6” = Package Services
-     * @param      $origin_zip      5 digit zip code.
-     * @param      $destination_zip 5 digit zip code.
-     * @param null $accept_date     string in the format dd-mmm-yyyy.
-     * @param null $accept_time     string in the format HHMM.
+     * @param string $originZip 5 digit zip code.
+     * @param string $destinationZip 5 digit zip code.
+     * @param string|null $acceptDate string in the format dd-mmm-yyyy.
+     * @param string|null $acceptTime string in the format HHMM.
+     *
+     * @return $this
      */
-    public function addRoute($mail_class, $origin_zip, $destination_zip, $accept_date = null, $accept_time = null): void
+    public function addRoute(int $mailClass, string $originZip, string $destinationZip, string $acceptDate = null, string $acceptTime = null): static
     {
         $route = [
-            'MailClass'      => $mail_class,
-            'OriginZIP'      => $origin_zip,
-            'DestinationZIP' => $destination_zip,
+            'MailClass'      => $mailClass,
+            'OriginZIP'      => $originZip,
+            'DestinationZIP' => $destinationZip,
         ];
-        if (!empty($accept_date)) {
-            $route['AcceptDate'] = $accept_date;
+
+        if ($acceptDate !== null) {
+            $route['AcceptDate'] = $acceptDate;
         }
-        if (!empty($accept_time)) {
-            $route['AcceptTime'] = $accept_time;
+
+        if ($acceptTime !== null) {
+            $route['AcceptTime'] = $acceptTime;
         }
+
         $this->route = $route;
+
+        return $this;
     }
 }
diff --git a/src/TrackConfirm.php b/src/TrackConfirm.php
index 7f84206..2b781fb 100644
--- a/src/TrackConfirm.php
+++ b/src/TrackConfirm.php
@@ -8,23 +8,23 @@
 class TrackConfirm extends USPSBase
 {
     /**
-     * @var string - the api version used for this type of call
+     * @var string the api version used for this type of call
      */
     protected string $apiVersion = 'TrackV2';
     /**
-     * @var string - revision version for including additional response fields
+     * @var string revision version for including additional response fields
      */
     protected string $revision = '';
     /**
-     * @var string - User IP address. Required when TrackFieldRequest[Revision=’1’].
+     * @var string User IP address. Required when TrackFieldRequest[Revision=’1’].
      */
     protected string $clientIp = '';
     /**
-     * @var string - Internal User Identification. Required when TrackFieldRequest[Revision=’1’].
+     * @var string Internal User Identification. Required when TrackFieldRequest[Revision=’1’].
      */
     protected string $sourceId = '';
     /**
-     * @var array - list of all packages added so far
+     * @var array list of all packages added so far
      */
     protected array $packages = [];
 
@@ -35,8 +35,6 @@ public function getEndpoint(): string
 
     /**
      * Perform the API call.
-     *
-     * @return string
      */
     public function getTracking(): string
     {
@@ -45,8 +43,6 @@ public function getTracking(): string
 
     /**
      * returns array of all packages added so far.
-     *
-     * @return array
      */
     public function getPostFields(): array
     {
@@ -63,11 +59,13 @@ public function getPostFields(): array
      *
      * @param string $id the address unique id
      *
-     * @return void
+     * @return $this
      */
-    public function addPackage(string $id): void
+    public function addPackage(string $id): static
     {
         $this->packages['TrackID'][] = ['@attributes' => ['ID' => $id]];
+
+        return $this;
     }
 
     /**
@@ -75,9 +73,9 @@ public function addPackage(string $id): void
      *
      * @param string|int $value
      *
-     * @return TrackConfirm
+     * @return $this
      */
-    public function setRevision(string|int $value): self
+    public function setRevision(string|int $value): static
     {
         $this->revision = (string)$value;
 
@@ -87,13 +85,11 @@ public function setRevision(string|int $value): self
     /**
      * Set the ClientIp value
      *
-     * @param string $value
-     *
-     * @return TrackConfirm
+     * @return $this
      */
-    public function setClientIp($value): self
+    public function setClientIp(string $value): static
     {
-        $this->clientIp = (string)$value;
+        $this->clientIp = $value;
 
         return $this;
     }
@@ -101,13 +97,11 @@ public function setClientIp($value): self
     /**
      * Set the SourceId value
      *
-     * @param string $value
-     *
-     * @return TrackConfirm
+     * @return $this
      */
-    public function setSourceId($value): self
+    public function setSourceId(string $value): static
     {
-        $this->sourceId = (string)$value;
+        $this->sourceId = $value;
 
         return $this;
     }
diff --git a/src/USPSBase.php b/src/USPSBase.php
index f2d300a..7fd3af8 100644
--- a/src/USPSBase.php
+++ b/src/USPSBase.php
@@ -149,11 +149,11 @@ public function setApiVersion($version): self
     /**
      * Set whether we are in a test mode or not.
      *
-     * @param bool $value
+     * @return $this
      */
-    public function setTestMode(bool $value): self
+    public function setTestMode(bool $value): static
     {
-        self::$testMode = (bool) $value;
+        self::$testMode = $value;
 
         return $this;
     }
@@ -327,7 +327,7 @@ public function setResponse(mixed $response = ''): self
     /**
      * Get the response data.
      */
-    public function getResponse(): mixed
+    public function getResponse(): string
     {
         return $this->response;
     }
diff --git a/src/ZipCodeLookup.php b/src/ZipCodeLookup.php
index 9ced8ea..646326b 100644
--- a/src/ZipCodeLookup.php
+++ b/src/ZipCodeLookup.php
@@ -2,27 +2,19 @@
 
 namespace USPS;
 
-/**
- * USPS Zip code lookup by city/state
- * used to find a zip code by city/state lookup.
- *
- * @since  1.0
- */
 class ZipCodeLookup extends USPSBase
 {
     /**
-     * @var string - the api version used for this type of call
+     * @var string the api version used for this type of call
      */
     protected string $apiVersion = 'ZipCodeLookup';
     /**
-     * @var array - list of all addresses added so far
+     * @var array list of all addresses added so far
      */
     protected array $addresses = [];
 
     /**
      * Perform the API call.
-     *
-     * @return string
      */
     public function lookup(): string
     {
@@ -31,8 +23,6 @@ public function lookup(): string
 
     /**
      * returns array of all addresses added so far.
-     *
-     * @return array
      */
     public function getPostFields(): array
     {
@@ -44,8 +34,10 @@ public function getPostFields(): array
      *
      * @param Address $data
      * @param string  $id   the address unique id
+     *
+     * @return $this
      */
-    public function addAddress(Address $data, $id = null): self
+    public function addAddress(Address $data, string $id = null): static
     {
         $packageId = $id !== null ? $id : ((count($this->addresses) + 1));