From time to time, an Invoice may not be properly created during the synchronization in QuickBooks. A record of the Invoice may show in QuickBooks, but the internal keys linking the Invoice to Acctivate may not exist. The next synchronization may properly create the Invoice in QuickBooks or Acctivate, but this will cause multiple Invoice to now show.
The solution is to simply delete both Invoices out of QuickBooks and run another synchronization. The synchronization should now properly create the correct Invoice in QuickBooks.
There are some variations to the scenario. For instance, the second synchronization may also create a duplicate invoice in Acctivate as well. Again, the solution to delete both invoices out of QuickBooks should remove the duplicate, errant Invoice from both Acctivate and QuickBooks.
If you continue to have problems with a duplicate Invoice, contact Acctivate Support by submitting a Support Request here.