A Refund follow-on transaction can be performed against a Purchase or a Completion to refund any part, or all of the transaction. Refund can only be performed on the same card used in the original Purchase or Completion transaction. Refund transactions should be sent using the original transaction’s Order ID and the Transaction Number returned in the original transaction response, and the amount. For processing refunds on a different card, the Independent Refund transaction should be used instead.
Go into configs to add credentials if they aren't there.