A remittance advice slip is a document sent from a customer to a supplier to indicate that invoices have been paid. The remittance advice slip includes invoice amounts and numbers, as well as any notes or changes that may have been necessary.
Suppliers can use remittance advice slips as a proof of payment, similar to the way in which a receipt is used. In some cases, suppliers create their own remittance advice slips that are included with an invoice. The customer can then remove the remittance advice slip and include it in the envelope with his payment to the supplier.