How to fix ‘The Invoice Number has already been taken’ error
The app requires that all invoices and quotes (even deleted ones) have a unique invoice number.
There are a few ways to resolve this error:
– Restore the deleted invoice, change the invoice number to a value you won’t use and then delete it again.
– Purge the client to fully delete the invoices.
– Purge the company on Settings > Account Management to fully delete all invoices.