The original Payment Txn record type needs to be one of:
- Direct Debit
- Manual
- Payment
- Events
- eCheck
AND the original Payment Txn field "TxnRef" (api name AAkPay__dpsTxnRef__c) must have a value.
The "original Payment Txn" means the Payment Txn record that you are trying to refund. This is the record that you'd press the refund button from.
The field "TxnRef" (api name AAkPay__dpsTxnRef__c) is automatically maintained by Payments2Us. If this is missing, then it might be related to a manual load of similar related activity.