Use case: Up-selling of ticket extras
-------------------------------------

Let's assume you're putting up a great music festival, and to save trouble with handling payments on-site, you want to sell parking spaces together with your ticket. By using our add-on feature, you can prompt all users to book the parking space (to make sure they see it) and ensure that only people with a ticket can book a parking space. You can set it up like this:

* Create a base product "Festival admission"
* Create a quota for the base product
* Create a category "Ticket extras" and check "Products in this category are add-on products"
* Create a product "Parking space" within that category
* Create a quota for the parking space product
* Go to the base product and select the tab "Add-Ons" at the top. Click "Add a new add-on" and choose the "Ticket extras" category. You can keep the numbers at 0 and 1.

During checkout, all buyers of the base product will now be prompted if they want to add the parking space.

.. tip::

   You can also use add-on products for free things, just to keep tabs on capacity.
