Authentication proxy as local radius for global protect


I wish to install Duo Authentication Proxy to integrate with my Palo Alto GlobalProtect gateway.
Documentation states: " This Duo proxy server also acts as a RADIUS server — there’s usually no need to deploy a separate additional RADIUS server to use Duo."

What IP address should I use for “host=x.x.x.x” under [radius_client] section inside config file? And where exactly is this Radius service running? I can’t locate Radius service running on my machine.