Part 1
Course reading
A return purchase order is used when goods must go back to the supplier — for example rejected quality, wrong material or over-delivery. In SAP you create a purchase order (ME21N) and tick the "Returns item" indicator on the line. This tells SAP that the goods movement will reduce stock instead of increasing it.
When the goods are shipped back, the warehouse posts the return with movement type 161 (goods issue for return PO) in MIGO. Stock goes down, the PO history shows the return and the supplier's invoice side expects a credit memo instead of an invoice. If 161 was posted by mistake, it is reversed with movement 162.
This is different from movement 122 (return delivery against an original goods receipt). Use 122 when you are reversing a specific receipt from the same delivery; use a return PO and 161 when the return is a separate business transaction, needs its own document for the supplier, or may require a returns delivery and shipping paperwork.
Example: 50 valves from a supplier fail inspection two weeks after receipt. Purchasing creates a return PO for 50, quality moves them to blocked stock, the warehouse posts 161 when the truck leaves, and accounts payable waits for the supplier credit memo. KPIs: supplier return rate, days to credit memo and value of open returns.