Failed to set remote answer sdp: Called in wrong state: stable

I am trying to write a WebRTC application using socket.io.

The signalling server is written in python and looks like this.

import socketio
import uvicorn
from starlette.applications import Starlette

ROOM = 'room'


sio = socketio.AsyncServer(async_mode='asgi', cors_allowed_origins='*')
star_app = Starlette(debug=True)
app = socketio.ASGIApp(sio, star_app)


@sio.event
async def connect(sid, environ):
    await sio.emit('ready', room=ROOM, skip_sid=sid)
    sio.enter_room(sid, ROOM)


@sio.event
async def data(sid, data):
    await sio.emit('data', data, room=ROOM, skip_sid=sid)


@sio.event
async def disconnect(sid):
    sio.leave_room(sid, ROOM)


if __name__ == '__main__':
    uvicorn.run(app, host='0.0.0.0', port=8003)

The client side looks like this

<script>
    const SIGNALING_SERVER_URL = 'http://127.0.0.1:8003?session_id=1';
    // WebRTC config: you don't have to change this for the example to work
    // If you are testing on localhost, you can just use PC_CONFIG = {}
    const PC_CONFIG = {};

    // Signaling methods
    let socket = io(SIGNALING_SERVER_URL, {autoConnect: false});

    socket.on('data', (data) => {
        console.log('Data received: ', data);
        handleSignalingData(data);
    });

    socket.on('ready', () => {
        console.log('Ready');
        // Connection with signaling server is ready, and so is local stream
        createPeerConnection();
        sendOffer();
    });

    let sendData = (data) => {
        socket.emit('data', data);
    };

    // WebRTC methods
    let pc;
    let localStream;
    let remoteStreamElement = document.querySelector('#remoteStream');

    let getLocalStream = () => {
        navigator.mediaDevices.getUserMedia({audio: true, video: true})
            .then((stream) => {
                console.log('Stream found');
                localStream = stream;
                // Connect after making sure that local stream is availble
                socket.connect();
            })
            .catch(error => {
                console.error('Stream not found: ', error);
            });
    }

    let createPeerConnection = () => {
        try {
            pc = new RTCPeerConnection(PC_CONFIG);
            pc.onicecandidate = onIceCandidate;
            pc.onaddstream = onAddStream;
            pc.addStream(localStream);
            console.log('PeerConnection created');
        } catch (error) {
            console.error('PeerConnection failed: ', error);
        }
    };

    let sendOffer = () => {
        console.log('Send offer');
        pc.createOffer().then(
            setAndSendLocalDescription,
            (error) => {
                console.error('Send offer failed: ', error);
            }
        );
    };

    let sendAnswer = () => {
        console.log('Send answer');
        pc.createAnswer().then(
            setAndSendLocalDescription,
            (error) => {
                console.error('Send answer failed: ', error);
            }
        );
    };

    let setAndSendLocalDescription = (sessionDescription) => {
        pc.setLocalDescription(sessionDescription);
        console.log('Local description set');
        sendData(sessionDescription);
    };

    let onIceCandidate = (event) => {
        if (event.candidate) {
            console.log('ICE candidate');
            sendData({
                type: 'candidate',
                candidate: event.candidate
            });
        }
    };

    let onAddStream = (event) => {
        console.log('Add stream');
        remoteStreamElement.srcObject = event.stream;
    };

    let handleSignalingData = (data) => {
        // let msg = JSON.parse(data);
        switch (data.type) {
            case 'offer':
                createPeerConnection();
                pc.setRemoteDescription(new RTCSessionDescription(data));
                sendAnswer();
                break;
            case 'answer':
                pc.setRemoteDescription(new RTCSessionDescription(data));
                break;
            case 'candidate':
                pc.addIceCandidate(new RTCIceCandidate(data.candidate));
                break;
        }
    };

    // Start connection
    getLocalStream();
</script>

Also i use this code for client as socket.io

https://github.com/socketio/socket.io/blob/master/client-dist/socket.io.js

When two people are in the connection, everything works great. But as soon as a third user tries to connect to them, the streaming stops with an error

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

I don't have much knowledge of javascript, so I need your help. Thanks.

P.S. I see this error in all browsers.

from Failed to set remote answer sdp: Called in wrong state: stable