How to charge inventory cost to a project, reduce stock, and track expense without changing the already invoiced project value in QuickBooks Online?

We are an EPC solar contracting company using QuickBooks Online. For each solar project, we invoice the client for the total project value (e.g., PKR 10 million). After invoicing, we use inventory items (like panels and inverters) during execution. We want to: Reduce inventory quantities used in the project Allocate their cost to the project for profitability tracking Keep the invoiced amount to the customer unchanged What is the correct workflow in QuickBooks Online to charge inventory at cost to a specific project (or sub-customer), reduce inventory stock, and reflect the expense in the project report — without altering the already issued customer invoice? Your guidance on the best practice for this scenario would be greatly appreciated.