Allowing access to Custom Post Types

The custom post types that can be queried must be explicitly configured. This can be done in 2 places.

In the Schema Configuration applied to the endpoint, by selecting option "Use custom configuration" under "Customize configuration, or use default from Settings?" and then selecting the desired items:

Selecting the allowed Custom Post Types in the Schema Configuration
Selecting the allowed Custom Post Types in the Schema Configuration

Or, if selecting option "Use configuration from Settings", the value defined under section "Included custom post types" in the Settings page for Schema Custom Posts is used:

Selecting the allowed Custom Post Types in the Settings
Selecting the allowed Custom Post Types in the Settings