Why the sync error occurs
This error occurs when you edit or delete a bill or invoice in Bill.com, but the related sales invoice or purchase invoice in Microsoft Dynamics 365 Business Central (MSDBC) is posted. Updates or deletions won't sync to posted transactions.
How to fix the sync error
Select to not sync the update to clear the error in Bill.com, or if the sales invoice/purchase invoice needs to be updated, delete in both Bill.com and MSDBC and recreate a new transaction with the correct details.