As of right now the invoice aspect and the projects are completely separate. Both functions exist is both Projects and in Books, but Projects is more elaborate, and the invoices created in Projects do not sync with Books. I would be great if I could connect a project from Projects to Zoho Books project and vice versa, so the invoicing is seen together as well as the time tracking for billable, and nonbillable hours.
This would also allow the same portal to be used for projects and Estimates/Invoices etc so that customers do not have to log into multiple areas to pay bills, see estimates, and follow projects.