The purpose of this operation is to refund the amount of a previous payment, crediting the cardholder account and debiting the Merchant account. 

A refund can be: 

Performed against a previous payment, referring its transactionID by sending a POST request over HTTPS to the /payments/{transactionID}/refund endpoint. 

Performed against a purchase (PURS) or captured pre-authorization (AUTH > Capture) payment types. 

It can be a full refund, when the total amount of the purchase is refunded to the cardholder, or a partial refund, when a subtotal of the purchase is refunded to the cardholder. 

POST /api/v2/payments/{transactionID}/refund