To enable this, create a smart collection named All Products and set the condition to 'Product price is greater than 0'. You can create a collection through the 'Collections' menu in Shopify admin. Or you can turn this section off through theme settings.
For some events we require people to pre-register. This is to ensure we have enough space for the amount of people coming or enough product for the amount of people coming, especially for events like prereleases.