There is a configuration issue: codecs not to be used in SIP as RTMP case should be listed in 'codecs_exclude_sip_rtmp' not removed from 'codecs'.
For example,
codecs =opus,alaw,ulaw,g729,speex16,g722,mpeg4-generic,telephone-event,h264,vp8,flv,mpv
codecs_exclude_sip =mpeg4-generic,flv,mpv...