The RADIUS server in the system settings in the webui is only for outgoing request, i.e. if privacyIDEA needs to send a RADIUS request to another radius server.
In your case you need to configure the file clients.conf which is probably located at /etc/freeradius/3.0/clients.conf. Also read: https://privacyidea.readthedocs.io/en/latest/application_plugins/index.html
Our company also provides an enterprise edition, which comes with an appliance tool, that helps you to set up things like RADIUS clients.