The default in Punchpass is to require customers to have an eligible pass credit in order to book a class, but you can adjust this on a class type basis. The universal setting is under Manage Settings > Online Reservations, but then within each class reservation setting you can turn this on/off.
Limit number of reservations to number of pass credits
Under Manage Settings > Online Reservations, within the Limitations section, make sure the Limit the # of reservations to visits purchased setting is selected. This is the default setting.
Require customers to have an active pass within the class settings
In the settings for each class, you'll find an option to require an active pass.
Here's how to turn that setting on:
From Manage Classes, click on the class, select the Actions dropdown and press Edit.
This takes you to the class overview page. Turn on the setting to require an active pass and press Save.
Note: If a customer drops in on a class, Punchpass will not remove a future reservation.
Instructors, staff, and other admin users can also book a customer's reservation regardless of their pass status. This is why is it is important to aways mark attendance and check for payment!