Return Deliveries 
Once a confirmation has been approved, you can return any part of the purchase order to the supplier if not satisfied with the goods.
Prerequisites
You have been assigned one of the following roles:
Operational Purchaser (portal role com.sap.pct.srm.ro_operationalpurchaser, SAP SRM Server role /SAPSRM/OP_PURCHASER)
Goods Recipient (portal role com.sap.pct.srm.ro_goodsrecipient, SAP SRM Server role /SAPSRM/RECIPIENT)
Activities
To return an item from a purchase order, you must create a Return Delivery document, clearly stating the reason for return. Once you return some or all of the items in a purchase order, the Return Delivery document is posted in the system. The quantity that is being returned is once again visible in the purchase order and is available for confirmation. This is because the system now expects a new delivery for this quantity from the supplier.
Note
Once an invoice is created, it is no longer possible to use the Return Delivery function.