Quickbooks Online solution. Since you cannot simply delete your client's credit card or replace it with a fake credit card number (which would still be confusing), we made a work around at our company. Under the Gear, select All Lists, then Payment Methods. Click "New" and create a new payment method named "No card on file" or what ever works best for your needs. Then, go back to your customer's account and where the drop-down menu for their card is, instead of selecting Visa, American Express, etc., select the new payment method you just created "No card on file."  Voila!