When cash or banktransfers receipts have to be corrected in the system, one needs to create a manual/Simple Post refund. This can also be the case if you simply need to correct the balance and no actual refund should be made on a credit card.
In the reservation go to the Billing Section:
In Type choose Refund:
Choose who should be on the invoice in To:
If there are more to choose from, click on the correct one:
Choose the correct cover reference (the applicable Invoice)
If the amount to refund is less than the cover reference (Sales Order/ Invoice) amount you can amend the amount in Total:
Lastly make sure the Invoice is credited (or credit partially when there is a partial refund, do this in New Billing):
