Why the sync error occurs
This error occurs when a bill is trying to sync to QuickBooks Online from Bill.com, and the vendor has different currencies assigned in QuickBooks Online and Bill.com. Vendor currencies must match between QuickBooks Online and Bill.com if multi-currency is enabled in QuickBooks Online.
How to fix the sync error
Vendor currency can't be changed in Bill.com once a bill is created for the vendor. Vendor currency can't be changed in QuickBooks Online either, once saved. To solve this error, a new vendor will need to be created in either QuickBooks Online or Bill.com with the desired currency.