[Serusers] strip realm_prefix & radius

Hi, I use RADIUS for user authentication. The SER configuration in REGISTER handler: if (!radius_www_authorize("")) { log(1, " - Radius Auth failed - Send challenge to UA"); www_challenge("", "0"); break; }; UAs are configured to use the realm 'domain.com'. There are cases (many UAs does not support DNS SRV) where UAs send 'sip.domain.com'. Which is the way to strip 'sip.' from realm and send it to RADIUS. I used the following : modparam("auth", "realm_prefix", "sip.") but it doesn't work. Actually, SER sends back '401 Unauthorized' with digest.realm="domain.com", and then UA sends REGISTER with realm="domain.com" but 'radius_www_authorize' fail. I see no RADIUS request to reach my RADIUS server. Any idea / help ? thank you Kosats