Project Billing customer how to account for COGS on Revenue

Our Customer uses Project Costing and Project Billing. Contract type of Projects are created.

All Purchases are against Project/Task and are charged to Project Cost GL control account and shown under current assets in Balance sheet.

Customer invoicing and revenue booking is done through Project Billing module into AR.

How is the COGS accounting done for this, so that the Project Cost GL control account is adjusted to the extent of the COGS on Revenue booked.? Is it done as a pre-approved expenditure batch or there are other options? Appreciate any help from PA consulting gurus.

Thanks

Gopal