Forticlient seems to have a lot of issues working correctly on Fedora and/or SAML required setups (where you complete the auth in an external browser). The best I can get from the error logs is that the connection was terminated. Fortinets support of Linux is not the best.
Fortunately you can sidestep most of the issues by using the openfortivpn and openfortivpn-webview packages. The first takes care of connecting and communicating to Fortinet based VPN services, while the latter provides compatibility with services requiring a SAML/cookie browser workflow. From here, you will only connect to the VPN via command line.
Start by installing both packages:
sudo dnf install openfortivpn openfortivpn-webviewWith those installed, the connection command will be this:
sudo openfortivpn VPN_HOSTNAME:VPN_PORT --username=VPN_USERNAME --realm=sso --cookie=$(/path/to/openfortivpn-webview.AppImage --url 'https://VPN_HOSTNAME:VPN_PORT/VPN_REALM' | sed -n 's/^SVPNCOOKIE=\(.*\)$/\1/p')Your values above may vary slightly depending on how your Fortinet VPN server is setup. I suggest saving this command as an alias, as it is quite long.
Note that when running this command, you must terminate it with CTRL-C to kill the connection. Closing the terminal won't quite do it. In that case, or if the connection is hung, you can track it down with htop and kill it.
It would be best if Fortinet just fixed their software for Linux, but this gets the job done.