if your config is OK, when you logon windows domain computer, user information must be collected by fortigate automatically and displayed on monitor section
it's working really what i did is removed the configration and re did again and it's working really the articul that you shared is the same that i follow it it's very recommended to work with it .
should show you which users are actually picked up.
I do recommend using the Agent based polling instead, leaves the FortiGate free for its firewalling job and is more flexible in terms of understanding logon events.
and another note: the firewall user monitor is important. If the user is not there or not correct, the policy objects WILL not work. First make sure the users are listed. If they are, then your firewall can use these groups in its policies.
