Capacity is the maximum number of allowed slots within a set up time frame. There may be many frames in a day so the number of customers’ bookings will reach the limit if you set a fixed stock quantity for booking products. That’s why you should allow your customers to order when products are out of stock.
Regarding products having variants:
- In the product edit page, edit the variant you would like
- Select “Continue selling when out of stock”
- Do similarly with the rest variants
Regarding products having no variant:
- On product edit page, select “Continue selling when out of stock”