WebRTC one-way communication by exposing the SDP of the sender

So on the offerer I have this code. It has a function which sends the SDP to the database.

const videoConstraints = {
  'video': true,
  'audio': false
}

var localStream = new MediaStream();

try {
  navigator.mediaDevices.getUserMedia(videoConstraints).then((stream) => {
    localStream = stream;
    video = document.getElementById("video");
    video.srcObject = stream;
  })
} catch (error) {
  console.log(error);
}

const turnConfig = {
  iceServers: [
//servers
  ]
}

const createOfferer = () => {
  var peer = new RTCPeerConnection(turnConfig);

  localStream.getTracks().forEach(track => {
    peer.addTrack(track, localStream);
  });

  peer.createOffer()
    .then((offer) => {
      fetch(window.location.href, {
        method: "POST",
        body: JSON.stringify(offer),
        headers: {
          "Content-Type": "application/json"
        }
      });
    })  
}

From there, the SDP is taken by the answerer, and then createAnswerer is called:

const setOnTrack = (peer, remoteVideo) => {
  var remoteStream = new MediaStream();

  remoteVideo.srcObject = remoteStream;

  peer.addEventListener('track', async (e) => {
    remoteStream.addTrack(e.track, remoteStream);
  })
}

const createAnswererForSeat = (offer) => {
  var peer = new RTCPeerConnection(turnConfig);

  var remoteVideo = createVideoForSeat(); //this function only creates the video element
  setOnTrack(peer, remoteVideo);

  peer.setRemoteDescription(offer)
    .then(() => {
      return peer.createAnswer();
    })
    .then((answer) => {
      peer.setLocalDescription(answer);
    });
}

For some reason, on Chrome there is no camera on answerer's side, and on Firefox I receive a WebRTC error.

Why is it not working? I am new to WebRTC, so if I'm missing something obvious sorry :)

Thanks.

In offerer you need to set local description after you create offer:

  peer.createOffer()
    .then((offer) => {
      peer.setLocalDescription(offer) // <--- here
      fetch(window.location.href, {
        method: "POST",
        body: JSON.stringify(offer),
        headers: {
          "Content-Type": "application/json"
        }
      });
    })  

In answerer you need to send the answer back to offerer and set it as a remote description there. Should be something like:

const onAnswer = async (answer) => {
    await peer.setRemoteDescription(answer)
}

Also, RTCPeerConnection should be stored somewhere outside callbacks, otherwise it will be garbage collected after the function exits.