Yes you need to set the negative quantities in the 95 lines. If you have used them however you cannot do this (but of course you cannot use something you do not have [:D])
It was already told. Go the Quantity tab in the purchase order lines - put the negative quantity in receive now and post the packing slip by changing quanity parameter to → Receive Now.
Yes - the packing slip will be disabled after receiving all the materials (when PO is in Received status).
But when you put the negative quantity in Receive now field the Packing Slip will be enabled.(Go the Quantity Tab in purchase order lines put negative quantity in Receive now field)…