When a customer pays online with a credit card, Kickserv records the payment as type "Credit Card (Online)". QuickBooks keeps its own list of payment types, and if you haven't taken a credit card payment before, QuickBooks might not have this payment type listed. So you'll need to add it. Here's how:
Open QuickBooks. Click Lists > Customer & Vendor Profile Lists. Select Payment Method List.
Click the Payment Method dropdown and choose New. The New Payment Method
dialog will open.
Name the new payment method "Credit Card (Online)" and select "Other Credit Card". Click OK.
The next time you sync with QuickBooks, the error should go away.