WebRTC Gathering problem

[venzonite]

Hi, I try to use WebRTC to establish p2p connection between 2 clients.
I have problem, because in browser's dev-tools I see the below error:
WebRTC: ICE failed, add a TURN server and see about:webrtc for more details

Full log from dev tools:

[2022-01-12T14:26:59.821Z] Information: Normalizing '/ViewerHub' to 'https://test.pl/ViewerHub'. signalr.min.js:16:34050

[2022-01-12T14:26:59.872Z] Information: WebSocket connected to wss://test.pl/ViewerHub?id=hHPbw0r1B6ZoLgiFaIiecA. signalr.min.js:16:34050

[2022-01-12T14:26:59.873Z] Information: Using HubProtocol 'messagepack'. signalr.min.js:16:34050

Rtc offer SDP received. ViewerHubConnection.ts:131:21

Ice candidate received. 2 ViewerHubConnection.ts:137:21

Set ICE candidate. 2 RtcSession.ts:96:16

Set RTC offer. RtcSession.ts:92:16

ICE candidate ready:  

RTCIceCandidate { candidate: "candidate:0 1 UDP 2122252543 7bde0dfd-c13f-4347-b2ce-ef7b437064ad.local 58598 typ host", sdpMid: "0", sdpMLineIndex: 0, usernameFragment: "a042c037" }

RtcSession.ts:70:20
ICE candidate ready:  

RTCIceCandidate { candidate: "candidate:3 1 TCP 2105524479 7bde0dfd-c13f-4347-b2ce-ef7b437064ad.local 9 typ host tcptype active", sdpMid: "0", sdpMLineIndex: 0, usernameFragment: "a042c037" }

RtcSession.ts:70:20

ICE connection state changed to checking RtcSession.ts:67:20

ICE candidate ready:  

RTCIceCandidate { candidate: "candidate:1 1 UDP 1686052863 217.96.44.130 55533 typ srflx raddr 0.0.0.0 rport 0", sdpMid: "0", sdpMLineIndex: 0, usernameFragment: "a042c037" }

RtcSession.ts:70:20

ICE candidate ready:  

RTCIceCandidate { candidate: "candidate:2 1 UDP 1686052351 217.96.44.130 38322 typ srflx raddr 0.0.0.0 rport 0", sdpMid: "0", sdpMLineIndex: 0, usernameFragment: "a042c037" }

RtcSession.ts:70:20

ICE candidate ready:  

RTCIceCandidate { candidate: "", sdpMid: "0", sdpMLineIndex: 0, usernameFragment: "a042c037" }

RtcSession.ts:70:20

ICE candidate ready:  null RtcSession.ts:70:20

Ice candidate received. 4 ViewerHubConnection.ts:137:21

Set ICE candidate. 4 RtcSession.ts:96:16

ICE connection state changed to failed RtcSession.ts:67:20

WebRTC: ICE failed, add a TURN server and see about:webrtc for more details

How to fix this?

[venzonite]

Solved problem.
Solution: STUN does not work behind symmetric NAT.