In cases where you need to retrieve a list of Payers, you can do it using query parameters in one of two ways depending on the type of Payer.
To retrieve the Payers that belong to a User, you will add the userId of the User to the above URL. If you wanted to get the Payers for a user with a userId of '971de944-a5f6-42e2-bdc2-af13313d1fae' you'd send a GET request to: /v1/payments/payers?userId=971de944-a5f6-42e2-bdc2-af13313d1fae
If you've elected to configure either Platform Payers or Partner Payers, this API may be less useful to you since the Payer is less likely to change by transaction. Nonetheless, you can retrieve a list of the Payers you've created by sending a GET request like so: /v1/payments/payers?payerType='PARTNER'
In either case, a successful response returns an array that contains identifying information for each of the Payers, including the PayerId, the name of the institution, and the last four digits of the account number.