Thanks for the clarification, Lukes_mum. The example is is helpful and I see exactly what you're looking for now. In this case, there isn't a shortcut around going back into the billable timesheet and re-marking it as billable in the system. Even though your invoice was deleted, the program still thinks you used the hours.
I know this causes a little extra legwork, and I recommend leaving feedback about it for our product development team. To do so, click Help in the top menu, then Send Feedback Online. We love hearing feedback from our users about ways we can enhance the program and facilitate managing your books.
Let me know if you have further questions!
