[SR-Users] Modify User-Agent Header in OPTIONS from Dispatcher Module

Hello all We are using topos in kamailio 5.5.6 to hide topology to some SIP-Servers. Now, I am trying to modify the User-Agent header of OPTIONS sent by Dispatcher Module, how is this possible? I tried something like this, because insert_hf or remove_hf does not work in event_route: # Branch cleanup branch_route[MANAGE_CLEANUP] {     remove_hf("User-Agent");     insert_hf("User-Agent: Test\r\n");     return; } # topos route event_route[topos:msg-sending] {     # Topology hiding for some hosts       if (is_request() and $sndto(ip)=="1.1.1.1") {         if (is_method("OPTIONS")) {             t_on_branch("MANAGE_CLEANUP");             t_relay();         }       } else {           # No topology hiding for other hosts...           drop;       } } But the branch-route is never called. I got two errors in Log: Apr  4 12:17:27 kamailio /usr/sbin/kamailio[32174]: CRITICAL: <core> [core/ip_addr.c:234]: ip_addr2sbuf(): unknown address family 0 Apr  4 12:17:27 kamailio /usr/sbin/kamailio[32174]: ERROR: tm [t_fwd.c:1752]: t_forward_nonack(): no branches for forwarding Any hints how to achieve this? Regards Stefan