For sites operating as an API server, you have to configure the clients that you are allowing access to post events. Only clients that match these client URLs and pass the API key you define will be allowed to post events.
API Key: You can set the API key for your site. This is an API key that any other site will need to have entered in their Endpoint settings in order to be allowed to post events on your site.
home_url() value of a site that you are granting permissions to post events to your site.
Label: How that site will be labeled when it is shown on your site as an event source or when filtering events.
Display on Calendar: Whether the display of events from these clients should default to ‘on’ or ‘off’. If ‘off’, the events will be hidden by default. They are still available, just not visible by default.
When your site is operating as a server, the My Calendar API Filters widget or
[my_calendar_api_sources] shortcode can be used to display controls for enabling and disabling events from the various sources (similar to the category filtering in the default calendar.)