Hello Sharvari,
The billing documents not generating COPA documents are probably related to Items (Materials) with certain item categories following special Requirement Types with Requirement Classes such that are configured for Sales Order Costing. In this case, the Sales Order Item (SDI) becomes a cost object. With such configuration, the COPA documents are not generated until you perform Results Analysis and Settlement for these Sales Order Items. I hope this is the case you're having. It's worth mentioning that in such occasions, it's advisable to activate the COPA on the Sales Order instead of the Billing Document. In this manner, the Sales Order Item is assigned to the PSG automatically (Check the assignment tab on the Sales Order Item if it's flagged in green). You may run reports from COPA showing Sales Orders-related data even without billing. It's as if you are getting planned/committed Sales in the COPA before arriving to Actuals.
Thanks.
Reda