|You must specify a different number. This number has already been used.|
This error occurs when Quickbooks preferences are set to prevent the invoice number of the bill or reference number offline payment to be reused if it has already been used for that same vendor.
If the error is for:
- A bill:
- Change the invoice number to something unique by clicking the Edit icon on the bill summary window
- An offline payment:
- Change the reference number to something unique by clicking the Edit icon on the bill payment information screen
Alternatively, you can adjust your QuickBooks preferences to allow use of duplicate invoice or payment fields.