Answer: Because the timesheet still needs to be encoded and linked to the corresponding sale order.

Explanation:
1. Verify Sales Order – Open the Sales Order and ensure the product is a service tracked by timesheets.

2. Check Product Settings – Under Sales > Products, confirm the Service Invoicing Policy is set to Based on Timesheets or Milestone.

3. Log Timesheets – Employees must log hours against the correct sales order/task in the Timesheets module.

4. Update Delivered Field – The 'Delivered' field auto-updates once timesheets match or exceed the ordered quantity.

5. Generate Invoice – Click Create Invoice, select the appropriate type, and confirm