The thread you suggested suggests it doesn’t work.
That said, I still tried. Networkmanager-vpnc requires a group name; which I don’t have.
NetworkManager-openconnect seems the one closest to working. I tried all variatons (including fortisslvpn) and nothing worked.
Just to let know others your suggestion doesn’t solve it. Thank you for trying, though.
I’ll try, as suggested at Reddit, to post at their forum and see if they give me a solution to this.