When a mistake occur, user could use FINANCE -> REVERSE PAYMENT to cancel a transaction. Please note that when a payment is created, there are entries being posted inside the corresponding cash books and general ledgers. When a reverse payment is triggered, the previous transactions remain in the cash books and general ledgers, new entries in opposite direction (of the same amount) is being created. Also take note that if the payment was used to knock off certain supplier invoices, or credit memo (both supplier and customer), these documents will become outstanding again when reverse payment is carried out.