Hello, not sure I got it, so to clarify: the problem is made by the 100 Trying arriving at the endpoint after 180 Ringing? Cheers, Daniel On 07.02.18 14:08, Matteo Campana wrote: Dear Kamailians, does anyone have any idea on the issue below? Alessio told me that is always reproducible, and he can also provide captures and more logs. Thanks in advance! Matteo *From: *sr-users &lt;sr-users-bounces(a)lists.kamailio.org&gt; on behalf of Alessio Miranda &lt;smirolandia(a)gmail.com&gt; *Reply-To: *"Kamailio (SER) - Users Mailing List" < sr-users(a)lists.kamailio.org&gt; *Date: *Tuesday, 16 January 2018 at 14:18 *To: *&quot;sr-users(a)lists.kamailio.org&quot; &lt;sr-users(a)lists.kamailio.org&gt; *Subject: *[SR-Users] Blind Transfer WS Error Hi, I have a problem with the blind transfer via WebSocket, debugging from the browser we see that in some cases when the REFER is done and the sip message "202 Accepted" arrives, the message "180 Ringing" arrives first and then the "100 Trying" and the transfer goes in error with "500 JsSIP Internal Error" I have an architecture with Kamailio in frontend and asterisk in backend on the same network, the sip dialogue between FE and BE is in SIP / UDP. The WebRTC client connects to WebSocket at Kamailio's public address. We have verified that the sip messages exchanged between kamailio and asterisk are always correct. Kamailio Ver. 4.4.4 Asterisk Ver. 13.18.3 PJSIP Ver. 2.6 JSSIP Ver. 3.2.2 Thanks Alessio _______________________________________________ Kamailio (SER) - Users Mailing Listsr-users@lists.kamailio.orghttps://lists.kamailio.org/cgi-bin/mailman/listinfo/sr-users -- Daniel-Constantin Mierlawww.twitter.com/miconda -- www.linkedin.com/in/miconda Kamailio Advanced Training - March 5-7, 2018, Berlin - www.asipto.com Kamailio World Conference - May 14-16, 2018 - www.kamailioworld.com