Navigate to Stores -> Configuration -> Sales -> Payment Methods.
The AfterPay payment methods are split per country.
For SOAP connection you will be provided with a Merchant ID, Portfolio ID and Password.
For REST connections you will be provided with an API key. There are designated payment methods for REST connections – Digital Invoice (REST).
For each AfterPay payment method you have a contract for, configure the options with the values as shown below. You need the account details as sent by AfterPay.
1) Enable the method
2) Fill in the maximum order value
3) Set Connection Mode to Test
4) For REST connections fill in the API key. Please choose the Connection type (Sandbox, Test, Production) and fill the corresponding API key.
For SOAP Connection fill in the Merchant ID, Portfolio ID and Password for test.