Why the Sync Error occurs
This error occurs when you link a bill to a PO in Bill.com and that link tries to sync to Sage Intacct, but the PO has items that require a Warehouse ID in Sage Intacct.
How to Fix the Sync Error
Bill.com doesn't currently support linking bills to POs in Sage Intacct when the PO is created using items that affect inventory control.
Delete the bill in Bill.com, and create the vendor invoice in Sage Intacct, allowing it to sync to Bill.com.