Why the Sync Error occurs
This error occurs when an invoice is trying to sync to QuickBooks Online (QBO) from Bill.com, but a product or service on the invoice has been deleted in QBO.
How to Fix the Sync Error
Check QBO for all the products and services listed on the invoice and make sure they are active. If you are not able to find a deleted item, the link between QBO and Bill.com may be broken. Please contact Customer Support in that case.