[Users] Passing predefined string-value to RADIUS accounting server

Hello All! I've encountered some difficulties. I need to pass predefined string value ("REALM" actually) to accounting RADIUS server. I want to did it in way similar to: modparam("acc", "radius_extra", "User-Name=$fU; Sip-User-Realm=$ar") But I need to set realm for all radius-accounting requests to some value ("MYREALM" for example). I tried set $ar explicitly before accounting this way $ar = "MYREALM"; but failed with error "invalid left operand in assignment". Does $ar read-only variable? Another my try was to pass new realm value in module configuration section: modparam("acc", "radius_extra", "User-Name=$fU; Sip-User-Realm=MYREALM") It failed with message "parse failed in <Sip-User-Realm=MYREALM> around position ..." I can't set up custom variable before route{} sections so I can't define my $var(realm) into module configuration line. Are any ways to solve my problem exists? -- With best regards!