edit main.js and change
window.RTC.rayo.pc[videobridge] = new window.RTC.peerconnection(null, {'optional': [{'DtlsSrtpKeyAgreement': 'true'}, {googIPv6: config.useIPv6}]});
to
window.RTC.rayo.pc[videobridge] = new window.RTC.peerconnection({ "iceServers": [{ "url": "stun:stun.l.google.com:19302" }] },
{'optional': [{'DtlsSrtpKeyAgreement': 'true'}, {googIPv6: config.useIPv6}]});