Fortinet

To troubleshoot problems it is important to understand the components involved in the captive portal user authorization process and the interactions between them.

Traffic Flow

Here is the traffic flow in the case of FortiGate firewall:

RADIUS Test

To test your RADIUS server You can go to User & Authentication -> RADIUS Servers. Select your RADIUS server and click on Test User Credentials. Here you can enter a username and password combination to see whether it passes RADIUS authorization or not.