I recently acquired a consultation job for a city as a designer/historian. The administrator set a flat rate fixed at $500 and the time grew way over than and I had to account for the extra hours. I gave them an invoice for an additional $500 then they requested to make $600 and resend it. But I sent it already and can't get the working slips back into the project manager. Does anyone have any ideas on fixing this that doesn't require manual data transferring?

Delete the invoice. You will be given the choice of turning the slips back into working slips. Choose yes, edit the slips again and create a new invoice. If you require the same invoice number don't forget to go into preferences and change it to the required number. Don't forget to change it back to the proper number afterwards.

HTH