Customer payment applied to the wrong invoice?

OK, a customer called me on Friday when they realized that a payment from a customer was entered, applied to an invoice and posted. Later they realized that it was applied to the wrong invoice. Could they correct it?

If the payment AND invoice has the status of OPEN (opposed to HIST or WORK), the payment can be reapplied to another OPEN invoice. If either the payment or the invoice is anything other than OPEN, you cannot change how the items are applied.

If both are OPEN, Open the Apply Sales Documents Window, open the customer and look up the Document that reduces the customer balance. From here you can click Unapply at the top or manually unapply one item at a time and apply the payment/return to a new invoice.