Accounts Payable lets you record an advance credit for goods that you have returned to a vendor, but the vendor has not yet received and has not yet issued a credit.
When you pay the invoice, you reduce your payment by the agreed amount , at the same time recording the advance credit for the returned goods.
The advance credit offsets the full amount of the invoice. However, because the vendor has not received either a payment or the goods, it preserves the outstanding balance for the unpaid portion of the invoice.
When the vendor issues the real credit note, you enter it in Invoice Entry, offsetting the advance credit in the vendor account.