Here's a VIDEO that may help you- How to create an appointment which is not billable or you can also use the following instructions to solve the issue.  


1. Go to "Appointments" located on the left menu. 


2. Click "Add Appointment" located on the top right of the calendar. 


3. Select your client and service type after the menu appears. 


4. Check the box "Do not bill" and then save. 


Final Product: