Here are a few key tips:

1. Group appointments use quantity purchased to track capacity. E.g., if a timeslot fits 15 people and a shopper purchases 2 spots in the same timeslot, available capacity for that timeslot will decrease from 15 to 13. 

2. A timeslot can only contain bookings of the same variant. E.g., if a product has two variants, Yoga - 30 Minutes and Yoga - 60 Minutes, and a booking is made for Yoga - 30 minutes at 4pm on Tuesday, that time can no longer be booked for Yoga - 60 minutes. 

3. Do not use different variants to specify different quantities of spots. E.g., for a group tour, do not create variants for 1 ticket, 2 tickets, 3 tickets, etc. Instead, create the product without variants and use the quantity field to allow shoppers to specify quantity of tickets needed.