QuickBooks Online sync error: Cannot delete Customer: This customer cannot be deleted because there are unbilled charges for this customer

Why the sync error occurs

This error occurs when a deleted customer in Key CashFlow℠ is trying to sync to QuickBooks Online, but the customer is linked to active/unbilled charges in QuickBooks Online.

How to fix the sync error

Reactivate the customer in Key CashFlow until the charges are completed in QuickBooks Online, or delete the unbilled charges in QuickBooks Online and sync again.