COGS matching with Revenue

Hello,

We are doing billing using a Project billing solution without having an order management module in scope.

The cost will be accumulated on the Projects from various sources like Payables invoice, Misc cost, and Inventory expense. We are using an event-based billing method for revenue recognition and invoice generation from PPM Contracts.

How to do COGS accounting in this scenario should be implemented and what should be the event for COGS recognition? If someone can provide stepwise accounting events and accounting entries to have COGS accounting in the above scenario that would be helpful.