Wix business solutions provide predefined slots for functions called function types. Function types define the integration points where you can add custom logic to extend the functionality of Wix apps like Wix Stores, Wix Bookings, and others.
You can only create functions from existing function types. Wix is always adding new function types, so there isn't a fixed list available. There are 2 ways to view available function types:
Calling Query Function Types returns all the function types available for a specific site. For example, if a site has only Wix Stores installed, the API returns only the function types that Wix Stores defines.
You can also filter your call by the business solution that defines the function type. For example, if a site has many apps installed but you want to retrieve only the function types defined by Wix Stores, you can use the Wix Stores app ID to filter the results.
On a site's Functions dashboard page there is a Functions catalog. This displays all the available function types based on the apps installed on the site. All sites with the same apps installed can use the same function types.