Simon Kiteley PRO said over 3 years ago on Video Chat with WebRTC :
Don't know if anyone has a clue... used as is. Using the numb server:

Uncaught (in promise) DOMException: Failed to execute 'createAnswer' on 
'RTCPeerConnection': PeerConnection cannot create an answer in a state other than 
have-remote-offer or have-local-pranswer.

Uncaught (in promise) DOMException: Failed to execute 'createAnswer' on 
'RTCPeerConnection': PeerConnection cannot create an answer in a state other than 
have-remote-offer or have-local-pranswer.

Uncaught (in promise) DOMException: Failed to execute 'setRemoteDescription' on 
'RTCPeerConnection': Failed to set remote answer sdp: Called in wrong state: kStable

Any help appreciated...