Hi, Probably need more details to give a correct answer, but I would try to keep it simple, using a combination of dispatcher module + updating $ru before relaying I believe would be a way to do this. Cheers, Joel. On Sat, May 23, 2020 at 14:35 christian (cx labs) &lt;christian(a)cxlabs.de <mailto:christian@cxlabs.de>> wrote: Hi, I'm trying to set up a Kamailio server as a proxy to forward SIP messages between two trunks, where I manipulate only the INVITE in the following manner: incoming call: INVITE +4969123456@server1 outgoing call: round robin to INVITE user@4969123456-sip-server2a INVITE user@4969123456-sip-server2b INVITE user@4969123456-sip-server2c Can anyone point me in the right direction? Both SIP trunks are IP registration only. Also, I am aware how strange this is, but the upstream service has decided to interpret SIP in a novel way. Cheers, Chris _______________________________________________ Kamailio (SER) - Users Mailing List sr-users(a)lists.kamailio.org <mailto:sr-users@lists.kamailio.org> https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users _______________________________________________ Kamailio (SER) - Users Mailing List sr-users(a)lists.kamailio.org https://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users