This error message normally occurs when there is a duplicate invoice detected in Sage 100 within an unposted batch.
To be classified as a duplicate the invoice number and vendor details in Sage will match those coded to the invoice being exported from SageAPA.
You should first confirm whether the invoice is a duplicate invoice.
You can use this article to see what batches are currently unposted in Sage and try to identify the batch number that is referenced in the error message.
If you find the same invoice in Sage 100, you can simply Mark the Invoice as Exported in SageAPA. Since the data is already in Sage 100, you do not need to export it again.
It is possible that the invoice is actually a different invoice. This sometimes happens with vendors who don't use unique invoice numbers.
In this scenario you should Reset the invoice in SageAPA and update the invoice number to something unique. Once you export and sync the invoice again, the invoice will populate in Sage 100 as it is no longer viewed as a duplicate.