Source Code: MasspaymentitemsApi
List Mass Payment Items (API Reference)
$massPaymentUrl = "https://api-sandbox.dwolla.com/mass-payments/eb467252-808c-4bc0-b86f-a5cd01454563";
$massPaymentItemsApi = new DwollaSwagger\MasspaymentitemsApi($apiClient);
$massPaymentItems = $massPaymentItemsApi->getMassPaymentItems($massPaymentUrl);
$massPaymentItems->total; # => "2"