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 (QBO) and sync cannot update or create the bill.
How to Fix the Sync Error
- In QBO, 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