Why the Sync Error occurs
This error occurs when the account, customer, item, vendor, and/or class on a bill (or the bill itself that is attempting to sync) has been deleted in QuickBooks Online and sync cannot update or create the bill.
How to Fix the Sync Error
- In QuickBooks Online, verify that the vendor and any accounts, customers, items, or classes listed on the payment has been deleted or determine if the bill was deleted
- Once the deleted entity is located, reactivate it
- Sync again