Nothing wrong with your configuration ,as long as you have the gateway and the billing on the same data subnet.
If the gateway is on I.P. 192.168.10.xxx, you are ready on the Quintum.
Try pinging the billing or radius server from the Quintum gateway.
Or enable the log of the Quintum to see the messages from/to radius.
Quintum# ev +rad to enable log
Quintum# ev -rad to disable log
Quintum# ev to display the log