diff --git a/packages/attestation-service/migrations/20211109200901-attestation-v8.js b/packages/attestation-service/migrations/20211109200901-attestation-v8.js
new file mode 100644
index 00000000000..60095627459
--- /dev/null
+++ b/packages/attestation-service/migrations/20211109200901-attestation-v8.js
@@ -0,0 +1,68 @@
+'use strict'
+
+module.exports = {
+  up: async (queryInterface, Sequelize) => {
+    const transaction = await queryInterface.sequelize.transaction()
+
+    try {
+      await queryInterface.removeIndex(
+        'Attestations',
+        ['ongoingDeliveryId'],
+        { fields: ['ongoingDeliveryId'], unique: true },
+        { transaction }
+      )
+      await queryInterface.addIndex(
+        'Attestations',
+        ['ongoingDeliveryId'],
+        { fields: ['ongoingDeliveryId'], unique: false },
+        { transaction }
+      )
+      await transaction.commit()
+    } catch (error) {
+      await transaction.rollback()
+      throw error
+    }
+  },
+  down: async (queryInterface, Sequelize) => {
+    const transaction = await queryInterface.sequelize.transaction()
+    try {
+      await queryInterface.removeIndex(
+        'Attestations',
+        ['ongoingDeliveryId'],
+        { fields: ['ongoingDeliveryId'], unique: false },
+        { transaction }
+      )
+      await queryInterface.addIndex(
+        'Attestations',
+        ['ongoingDeliveryId'],
+        { fields: ['ongoingDeliveryId'], unique: true },
+        { transaction }
+      )
+    } catch (error) {
+      await transaction.rollback()
+      if (
+        error.errors.length == 1 &&
+        error.errors[0].path == 'ongoingDeliveryId' &&
+        error.errors[0].type == 'unique violation'
+      ) {
+        try {
+          console.warn('Duplicates in ongoingDeliveryId; nulling out column and retrying.')
+          await queryInterface.removeColumn('Attestations', 'ongoingDeliveryId')
+          await queryInterface.addColumn('Attestations', 'ongoingDeliveryId', {
+            type: Sequelize.STRING,
+            allowNull: true,
+          })
+          await queryInterface.addIndex(
+            'Attestations',
+            ['ongoingDeliveryId'],
+            { fields: ['ongoingDeliveryId'], unique: true },
+            { transaction }
+          )
+        } catch (error) {
+          await transaction.rollback()
+          throw error
+        }
+      }
+    }
+  },
+}
diff --git a/packages/attestation-service/src/db.ts b/packages/attestation-service/src/db.ts
index ddee3204dcf..066e718ca22 100644
--- a/packages/attestation-service/src/db.ts
+++ b/packages/attestation-service/src/db.ts
@@ -322,6 +322,8 @@ export async function findAttestationByDeliveryId(
 ): Promise<AttestationModel | null> {
   return (await getAttestationTable()).findOne({
     where: { ongoingDeliveryId },
+    // Ensure deterministic result, since deliveryId uniqueness is not enforced
+    order: [['createdAt', 'DESC']],
     ...options,
   })
 }
diff --git a/packages/attestation-service/src/sms/twilioVerify.ts b/packages/attestation-service/src/sms/twilioVerify.ts
index cfe4772526c..77fe228f75e 100644
--- a/packages/attestation-service/src/sms/twilioVerify.ts
+++ b/packages/attestation-service/src/sms/twilioVerify.ts
@@ -108,6 +108,10 @@ export class TwilioVerifyProvider extends TwilioSmsProvider {
         requestParams.locale = locale
       }
     }
+
+    // Note: SID returned by Verify API is not unique for a phone number (within a 10 min interval)
+    // i.e. re-requests to the same phone number in <10 min will return an exisiting SID
+
     try {
       const m = await this.client.verify
         .services(this.verifyServiceSid)
diff --git a/packages/attestation-service/test/__mocks__/twilio.ts b/packages/attestation-service/test/__mocks__/twilio.ts
index d45160dc419..49cb41174f5 100644
--- a/packages/attestation-service/test/__mocks__/twilio.ts
+++ b/packages/attestation-service/test/__mocks__/twilio.ts
@@ -6,6 +6,7 @@ export const mockVerifyCreate = jest.fn((_obj: Object) => {
     sid: undefined,
   }
 })
+export const mockVerifyUpdate = jest.fn()
 export const mockMessagesCreate = jest.fn((_obj: Object) => {
   return {
     sid: undefined,
@@ -28,9 +29,16 @@ const twilio = jest.fn().mockImplementation((_twilioSid, _twilioAuthToken) => {
       services: Object.assign(
         (_sid: string) => {
           return {
-            verifications: {
-              create: mockVerifyCreate,
-            },
+            verifications: Object.assign(
+              (_sid: string) => {
+                return {
+                  update: mockVerifyUpdate,
+                }
+              },
+              {
+                create: mockVerifyCreate,
+              }
+            ),
           }
         },
         {
diff --git a/packages/attestation-service/test/sms/twilio.test.ts b/packages/attestation-service/test/sms/twilio.test.ts
index 9f8d564c946..2f3215c6072 100644
--- a/packages/attestation-service/test/sms/twilio.test.ts
+++ b/packages/attestation-service/test/sms/twilio.test.ts
@@ -1,16 +1,20 @@
+import { SmsFields } from '../../src/models/attestation'
 import { TwilioMessagingProvider, TwilioVerifyProvider } from '../../src/sms/twilio'
 import { mockMessagesCreate, mockVerifyCreate } from '../__mocks__/twilio'
 
 jest.mock('../__mocks__/twilio')
 
 describe('TwilioSmsProvider tests', () => {
-  describe('sendSms', () => {
-    const twilioSid = 'twilioSid-123!'
-    const verifyServiceSid = 'verify-sid-123!'
-    const twilioAuthToken = 'fakeAuth-123!'
-    const unsupportedRegionCodes = ['GH', 'IJ', 'KL']
-    const messagingServiceSid = 'messagingId-123!'
-    const attestation = {
+  const twilioSid = 'twilioSid-123!'
+  const verifyServiceSid = 'verify-sid-123!'
+  const twilioAuthToken = 'fakeAuth-123!'
+  const unsupportedRegionCodes = ['GH', 'IJ', 'KL']
+  const messagingServiceSid = 'messagingId-123!'
+  let attestation: SmsFields
+
+  beforeEach(() => {
+    jest.clearAllMocks()
+    attestation = {
       account: '0x123',
       identifier: '0x456',
       issuer: '0x789',
@@ -22,34 +26,29 @@ describe('TwilioSmsProvider tests', () => {
       appSignature: undefined,
       language: 'en',
     }
-
-    beforeEach(() => {
-      jest.clearAllMocks()
-    })
-
-    it('should initialize and send SMS via TwilioVerifyProvider', async () => {
-      const twilioVerifyProvider = new TwilioVerifyProvider(
-        twilioSid,
-        twilioAuthToken,
-        unsupportedRegionCodes,
-        verifyServiceSid
-      )
-      await twilioVerifyProvider.initialize('fake-delivery-status-url')
-      await twilioVerifyProvider.sendSms(attestation)
-      expect(mockVerifyCreate).toBeCalledTimes(1)
-      expect(mockMessagesCreate).not.toBeCalled()
-    })
-    it('should initialize and send SMS via TwilioMessagingProvider', async () => {
-      const twilioMessagingProvider = new TwilioMessagingProvider(
-        twilioSid,
-        twilioAuthToken,
-        unsupportedRegionCodes,
-        messagingServiceSid
-      )
-      await twilioMessagingProvider.initialize('fake-delivery-status-url')
-      await twilioMessagingProvider.sendSms(attestation)
-      expect(mockMessagesCreate).toBeCalledTimes(1)
-      expect(mockVerifyCreate).not.toBeCalled()
-    })
+  })
+  it('should initialize and send SMS via TwilioVerifyProvider', async () => {
+    const twilioVerifyProvider = new TwilioVerifyProvider(
+      twilioSid,
+      twilioAuthToken,
+      unsupportedRegionCodes,
+      verifyServiceSid
+    )
+    await twilioVerifyProvider.initialize('fake-delivery-status-url')
+    await twilioVerifyProvider.sendSms(attestation)
+    expect(mockVerifyCreate).toBeCalledTimes(1)
+    expect(mockMessagesCreate).not.toBeCalled()
+  })
+  it('should initialize and send SMS via TwilioMessagingProvider', async () => {
+    const twilioMessagingProvider = new TwilioMessagingProvider(
+      twilioSid,
+      twilioAuthToken,
+      unsupportedRegionCodes,
+      messagingServiceSid
+    )
+    await twilioMessagingProvider.initialize('fake-delivery-status-url')
+    await twilioMessagingProvider.sendSms(attestation)
+    expect(mockMessagesCreate).toBeCalledTimes(1)
+    expect(mockVerifyCreate).not.toBeCalled()
   })
 })