Before you can start booking people into group appointments, you'll have to make sure that you "reserve" space for them—essentially, "prebooking" the group time slot first, and then adding patients later. Here's how to set that up!
Add group appointments to your calendar
Head to the Appointments page, and find the date you wish to book the class appointment for (you can use the arrows to toggle between months, and the blue circle will indicate the selected date):
Click on the day and time slot that you want to add the group appointment, and select the appropriate one from the drop-down list of available appointment types:
You'll notice that when you select a group appointment type, the field for the patient name disappears. This is supposed to happen!
Set the appointment to repeat if need be (this is handy for classes, if you're offering a weekly pilates class on the same day, at the same time every week, for example!).
Then, click Create group appointment type, and you will see it show up on your calendar:
You'll notice that it says 0/number in the upper-right corner. The number is the number of patients that can attend that group appointment. You can alter this number, if you want, just for this particular appointment. When you're adding the appointment to your calendar, just change the number in the "Max. patients" field, as in the example below.
And that's it. You now have some open group appointments in which you can book patients into!