Hello Theodor, I looked into the provided trace. It seems that the multi-part body is here making issues. The header part Content-Length is updated, but not the multi-part one. There have been other issues with multipart body messages before, as its not used that often. It might be a bug/limitation in the rtpengine module. If nobody else comment you could open an issue about it to not forget about it. Cheers, Henning -- Henning Westerholt - https://skalatan.de/blog/ Kamailio services - https://gilawa.com<https://gilawa.com/> From: Scherney Theodor &lt;Theodor.Scherney(a)kontron.com&gt; Sent: Mittwoch, 2. August 2023 09:44 To: Kamailio (SER) - Development Mailing List &lt;sr-dev(a)lists.kamailio.org&gt; Subject: [sr-dev] rtpengine_manage - Rewrite SDP body Hello, The Problem is that SDP body is rewritten, but Content-Length isn't updated. Attached a trace from PCSCF. Event 207 Incoming INVITE: Content length of SDP body is 313. [cid:image001.png@01D9CED6.1DD91730] Event 218 Outgoing INVITE: SDP body is rewritten triggered by "rtpengine_manage". [cid:image002.png@01D9CED6.1DD91730] Content length of SDP body isn't updated. It should be 242. Event 212: Received from RTP Proxy [cid:image003.png@01D9CED6.1DD91730] Kamailio Version 5.5.X LOGs from rtpengine.c: Changed File according Logs attached.. 2023-08-01T10:25:41.118366+02:00 172.29.21.25 vict-pcscf-rhel8[1170319] - [logSDID@20306 resource="rtpengine"] ERROR: rtpengine [rtpengine.c:4070]: newbody 'v=0#015#012o=- 3863667612 3863667612 IN IP4 172.23.12.62#015#012s=pjmedia#015#012b=AS:84#015#012t=0 0#015#012a=X-nat:0#015#012m=audio 30444 RTP/AVP 8 101#015#012c=IN IP4 172.29.21.32#015#012b=TIAS:64000#015#012a=sendrecv#015#012a=rtpmap:8 PCMA/8000#015#012a=rtpmap:101 telephone-event/8000#015#012a=fmtp:101 0-16#015#012' 2023-08-01T10:25:41.118730+02:00 172.29.21.25 vict-pcscf-rhel8[1170319] - [logSDID@20306 resource="rtpengine"] ERROR: rtpengine [rtpengine.c:4071]: newbody.len [242] 2023-08-01T10:25:41.119049+02:00 172.29.21.25 vict-pcscf-rhel8[1170319] - [logSDID@20306 resource="rtpengine"] ERROR: rtpengine [rtpengine.c:4110]: rtpengine_offer_answer-03 Any suggestions on how to solve this problem? Thanks! BR Theo