Why the sync error occurs:

This error occurs when an item is marked as billable on a bill in Bill.com, but the box "I sell this product/service to my customers" isn't selected on the Item in Quickbooks Online.

How to fix the sync error:

In Bill.com, toggle the billable box off for the item on the bill

OR

In Quickbooks Online, select the box for "I sell this product/service to my customers" and assign an income account to the item that's shown in the error.

1. In Quickbooks Online, go to the Sales menu and select the Products and Services tab.
2. Select Edit for the item.
3. Select the I sell this product/service to my customers checkbox.
4. Select the Income account dropdown and select the account you want to use to track the sale.
5. Select Save and Close.