I'm running Magento CE 220.127.116.11 and using the standard Paypal API/Payment gateway and I am trying to credit a credit memo on an invoice and I receive the following error:
Required parameter missing: sale_or_invoice_id
The screen shows New Credit Memo for Order #100000009 and making sure I am crediting back the product of cost $2.65 with qty 1 etc...
I click on the Refund button (not Refund Offline) and it gives me back the error above. However, somehow Paypal receives the refund requests and refunds the transaction! Magento does not show the credit nor the credit memo.