QuickBooks Online sync error: Invalid Reference Id : Categories cannot be used in transactions

Why the sync error occurs

This error occurs when a bill with items in Key CashFlow is attempting to sync to QuickBooks Online, but the type of one or more of the items is set as Category in QuickBooks Online. You can't use category items on bills in QuickBooks Online.

How to fix the sync error

Edit the bill in Key CashFlow and select a product or service item for each line item, and sync again.