There is nothing to invoice!
Reason(s) of this behavior could be:
- You should deliver your products before invoicing them: Click on the "truck" icon (top-right of your screen) and follow instructions.
- You should modify the invoicing policy of your product: Open the product, go to the "Sales" tab and modify invoicing policy from "delivered quantities" to "ordered quantities". For Services, you should modify the Service Invoicing Policy to 'Prepaid'.