Payengine:
Endpoint to refund a capture transaction referencing the corresponding orderId and transactionId.
A refund transaction can only be applied to a capture transaction that is in status SUCCESS. Partial refunds are supported but the initialAmount cannot be higher than the amount that was captured.
More info: Refund request
Paygate:
The equivalent can be found here: REST API - Swagger#/Payments/refundPayment