Getting erro with webrtc

[SendOTP]

== Using SIP RTP CoS mark 5
[Jun 30 15:20:06] WARNING[13537][C-00000008]: chan_sip.c:10623 process_sdp: Rejecting secure audio stream without encryption details: audio 49381 RTP/SAVPF 111 103 104 0 8 106 105 13 126

I am getting this error when using webRtc with asterisk 12

any idea why this happens