Like invoices, payment requests are paid by the payment program when the due date is reached. The system also checks to ensure that the corresponding invoice is not scheduled to be paid in the next payment run, and has not already been paid. If a payment request cannot be made for one of the reasons already mentioned, it will appear on the payment proposal exception list. In such a case, you should cancel the request, since payment cannot be made.
You can also make partial payments for previously posted invoices. To do this, you first block the invoice from payment, and then enter a payment request for the partial amount.