This functionality is available as a customization using VBA/API.  We also offer customization services. For more information, contact your account manager.

OR

Run a query to show all invoices in the system and manually review the results for duplicates:
 

  1. Create a new invoice query
  2. Leave the Criteria tab blank
  3. On the Output tab, expand Invoice and select Invoice Number
  4. Select any other information to include in the results
  5. On the Sort tab, select Invoice Number
  6. Select the Results tab and review the results for duplicate invoice numbers