I am sharing this article that I authored, it is published in Eursap.eu
Debit items can be posted on a vendor by creating a down payment or posting a credit memo on the vendor. For the purpose of our demonstration we assume that the debit item is created by a down payment.
The down payment process starts with the creation of a down payment request. You create a down Payment request with transaction F-47, either directly in AP, or with link to the Purchase order.
Assume again that in our case, we are creating a down payment request directly from FI-AP without reference to a PO Created from MM.