I am investigating this also. It is call Third Party Processing in the documentation. The Item Category TAS in the Sales Order will create a Purchase Requisition with the Customer Delivery Address. You create a PO from the Purchase Req. It is not set up in my system, so I’m not sure how the Inventory is handled, but it is different from standard.
There is also Item Category TAB that is similar, but is designed to bring into your warehouse as reserved stock for that specific Sales Order.
if u want the system to create PO automatically
1. create third party sales order mean SO with TAS item category (in material master pls assign genral item category BANS in basic data 1 view) system will pick the TAS item category automatically.
2. In item category of SD u can even define to create automatic PO instant of PR. PO/PR create once u save the SO