Hello, function couldnt probably validate parameter. Could you share your function line. Best Regards Yasin CANER if ( subst_body("/^o=(.*) /o=$fU /") ) {}; or $avp(regx)="/^o=(.*)/o=$fU/"; if ( subst_body("$avp(regx)") ) {}; ________________________________ From: sr-users &lt;sr-users-bounces(a)lists.kamailio.org&gt; on behalf of Kristijan Vrban &lt;vrban.lkml(a)gmail.com&gt; Sent: Wednesday, February 20, 2019 6:00 PM To: Kamailio (SER) - Users Mailing List Subject: [SR-Users] Regex issue with subst_body Hi, in a sdp i need to rewrite a a=sendrecv to a=sendonly but onyl for the for the video stream. I made a regex like this: (?<=m=video)(?s)(.*)(a=sendrecv) Full version here: https://regex101.com/r/rovecJ/1 But if have problems to translate this into kamailio config via subst_body function. I always end with ERROR: fix_actions(): fixing failed (code=-3) Somebody sees the mistake? Kristijan _______________________________________________ Kamailio (SER) - Users Mailing List sr-users(a)lists.kamailio.org https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users