HI nikmagashi,
I am not quite sure but may it be possible that you have to put the RADIUS key in the secret field under RADIUS server and the other field is just for a shared secret that you choose for your cilents to establish the VPN connection?
So you can choose the shared secret and have to put in in when establishing the connection.
The final authentication is against the radius server.
I havent configured this before... so its just an idea 🙂
Kind Regards
Niklas