Hi,
In Your above reply You are absolutely doing correct steps,
It is done as follow:
PO created for JBW (e.g raw material supplier)
Subcontract PO created for SC1 (Subcontracting Vendor)
JBW sends material to SC1. Upon receipt of material at SC1 GR done. Mat Doc - 001
Challan created wrt to 001. Challan No - 901
SC1 assembles and needs to send to SC2. When SC2 confirms material receipt GR done. Mat Doc 002. Challan 901 reconciled and another challan created 902 (For goods sent to SC2)
SC2 Assembles and send it to Plant finally .... (at last)
You Have to use Mat doc 002 to create challan 902.
Regards
Satish