We created a report based on Invoice Detail template to display the information that we would like to send to clients as part of their invoice. We did this because we see that no actual invoice document gets created when you create an invoice in the Billings tab. Ideally we would like an invoice document to be created when we create an invoice in Billings, and that the invoice document picks up all the relevant information from the client and project that we are billing (ie. client address, purchase order number etc.).