This means an invoice or credit note has been deleted from Exact Online but not from Teamleader. During the synchronisation, we fetch the booking number from Exact Online and store it in Teamleader. In Exact Online, the number will always be the number of the last booking +1. If a booking has been deleted from Exact Online, but not from Teamleader, this will cause the same number to be added to Teamleader during the next sync for different invoices or credit notes.


Just follow those steps carefully to fix this error. In case you might be unsure on how to use your Exact Online account, then do show this article to your accountant.

  1. Navigate to your user icon in the top right hand corner > Click "Integrations"
  2. Click on "Explore" and search for "Exact Online"
  3. Click on "Manage" > "Deactivate"
  4. Be sure to NOT delink the contacts
  5. Fill in a delink date, this needs to be the date of the deleted invoice that caused the error.
  6. Go to Exact Online and delete all invoices after and including the invoice that causes the error. This is very important as otherwise duplicates will be generated. Do note that if you have credit notes on and after the delink date you'll need to delete these credit notes from Exact Online too! 
  7. Go back to Teamleader > your name/picture in the top right hand corner > Click "Integrations"
  8. Click on "Explore" and search for "Exact Online"
  9. Click on "Add"
  10. Fill in the date of the very first invoice in Teamleader as start date.
  11. Go to "Invoices" > Click on the synchronisation button (two arrows) in the bar at the top
  12. All your invoices from Teamleader will be synced with your Exact Online account.