You will find the Rest API Extended settings on your WordPress admin area navigating to the GamiPress menu -> Settings -> Add-ons tab.

Base URL
Sets the base URL from all endpoints of this add-on will be accesible. By default, gamipress.
If you change this setting to “my-api” then an add-on endpoint like /wp/v2/gamipress/get-points will change to /wp/v2/my-api/get-points.

Allow GET parameters
By default, all routes accepts POST parameters only. Check this option to allow GET parameters too (useful for testing purposes).