A quote cannot be issued requesting payment. The client's accounting department will not accept the quote as a demand for payment. They always match purchase orders with invoices to verify they are paying for whatever has been requested. Differences between the PO and the invoice must be explained and approved by management before the invoice can be paid.   The supplier may issue a receipt showing the details of the most recent payment from the client and indicate any differences or money still owed by the client. The receipt confirms to the client that the supplier has received the stated funds from the client.