"This ID has already been used" error message

[TribecaCitizen]

I keep getting an error message saying "This ID has already been used" when I try to send an invoice. No clue what that even means.

[Sean]

@TribecaCitizen - So sorry for the delay in following up! Were you customizing the "Invoice ID" field when you were creating it? It sounds like this number may have already matched an outstanding/previous invoice.