QuickBooks Online sync error: Invalid entity data. Email: Invalid email format.

Why the sync error occurs

This error occurs when a customer in QuickBooks Online is trying to sync to Key CashFlow, but there are multiple email addresses in the email field.

How to fix the sync error

Delete all but one email address for the customer in QuickBooks Online, and sync.

To prevent this error, enter only one email address for each customer when entering the customer details in QuickBooks Online.