Synapse 1.150.0 does not expose MatrixRTC transports endpoint despite msc4143_enabled=true

[sdestem]

Description

I am trying to enable MatrixRTC (MSC4143) with Element Call + LiveKit on a self-hosted setup, but the endpoint /_matrix/client/v1/rtc/transports is not recognized by Synapse.

Setup

• Synapse deployed via matrix-docker-ansible-deploy
• Element Web + Element Call
• LiveKit + lk-jwt-service working
• Reverse proxy: Traefik (playbook-managed)

Configuration

In homeserver.yaml:

experimental_features:
  msc4143_enabled: true

matrix_rtc:
  transports:
    - type: livekit
      livekit_service_url: "https://rtc.kimiu.fr/livekit/jwt"

Well-known

https://kimiu.fr/.well-known/matrix/client returns:

{
  "m.homeserver": {
    "base_url": "https://matrix.kimiu.fr",
    "server_name": "kimiu.fr"
  },
  "org.matrix.msc4143.rtc_foci": [
    {
      "type": "livekit",
      "livekit_service_url": "https://rtc.kimiu.fr/livekit/jwt"
    }
  ]
}

LiveKit

Health endpoint works:

curl https://rtc.kimiu.fr/livekit/jwt/healthz → HTTP 200

Problem

This request returns 404 / M_UNRECOGNIZED:

curl -i https://matrix.kimiu.fr/_matrix/client/v1/rtc/transports \
  -H "Authorization: Bearer <access_token>"

Response:

{
  "errcode": "M_UNRECOGNIZED",
  "error": "Unrecognized request"
}

Expected

Synapse should expose the MatrixRTC transport endpoint when MSC4143 is enabled.

Notes

• Synapse config clearly includes msc4143_enabled: true
• matrix_rtc block is present in homeserver.yaml
• Synapse has been restarted after config changes

Is there an additional flag or requirement to enable this endpoint?

Thanks

Steps to reproduce

• list the steps
• that reproduce the bug
• using hyphens as bullet points

Homeserver

matrix.kimiu.fr (self-hosted)

Synapse Version

1.150.0

Installation Method

Docker (matrixdotorg/synapse)

Database

PostgreSQL (single server, no SQLite migration, no backup restore)

Workers

Single process

Platform

Debian 12 (OVH VPS), Synapse running in Docker via matrix-docker-ansible-deploy, Traefik reverse proxy, LiveKit + lk-jwt-service for MatrixRTC

Configuration

MSC4143 enabled (experimental_features.msc4143_enabled: true)

matrix_rtc configured with LiveKit:
matrix_rtc:
  transports:
    - type: livekit
      livekit_service_url: "https://rtc.kimiu.fr/livekit/jwt"

No custom modules, no unusual presence or message retention settings.

Relevant log output

No relevant errors found in Synapse logs.

The issue is reproducible via API:

curl -i https://matrix.kimiu.fr/_matrix/client/v1/rtc/transports \
  -H "Authorization: Bearer <access_token>"

Response:

HTTP/2 404

{"errcode":"M_UNRECOGNIZED","error":"Unrecognized request"}

Anything else that would be useful to know?

Element Call standalone (https://call.kimiu.fr) works correctly.

LiveKit and JWT service are reachable and healthy:
https://rtc.kimiu.fr/livekit/jwt/healthz → HTTP 200

The .well-known/matrix/client endpoint is correctly configured and returns the expected RTC config.

The issue only affects the MatrixRTC integration via Synapse.

[escix]

The output from this needs to be in JSON format (Check for matrix.org for example. https://matrix.org/.well-known/matrix/client).

https://kimiu.fr/.well-known/matrix/client returns:

{
  "m.homeserver": {
    "base_url": "https://matrix.kimiu.fr/",
    "server_name": "kimiu.fr"
  },
  "org.matrix.[msc4143](https://github.com/matrix-org/matrix-spec-proposals/pull/4143).rtc_foci": [
    {
      "type": "livekit",
      "livekit_service_url": "https://rtc.kimiu.fr/livekit/jwt"
    }
  ]
}

[devastgh]

The output from this needs to be in JSON format

And needs to have the CORS headers explicitly described in the documentation.
Without them, it will not work. And today, /_matrix/client/v1/rtc/transports is not even necessary to use element-call.

[playerro]

So there are no ways to setup calls until the issue will not be fixed?

[escix]

This is what yours returns vs what it should be as per matrix.org

[pdanzma]

Confirming this on a fresh setup - Synapse 1.158.0

Same symptom, different environment:
matrix_rtc: transports: - type: livekit livekit_service_url: "https://<redacted>/lk-jwt"

• experimental_features.msc4143_enabled: true set
• matrix_rtc.transports block present and syntactical correct
• /_matrix/client/versions correctly reports "org.matrix.msc4143": true
• .well-known/matrix/client correctly returns the org.matrix.msc4143.rtc_foci block
• Synapse fully restarted after config changes
• Bare-metal Debian install (no docker), reverse proxy: nginx

Both endpoint variants fail identically:
GET /_matrix/client/v1/rtc/transports

{"errcode":"M_UNRECOGNIZED","error":"Unrecognized request"}

No relevant errors in journalctl -u matrix-synapse. So the advertisement flag (/versions, .well_known) is working correctly, but the actual REST resource for the transports endpoint doesn't seem to be registered at all, same disconnect as reported here. Any update on wheather this is a known regression or mission registration in the ressource dispatcher?

Thanks in advance!

[dvergeylen]

Both endpoint variants fail identically: GET /_matrix/client/v1/rtc/transports

{"errcode":"M_UNRECOGNIZED","error":"Unrecognized request"}

That endpoint seems to fail, but _matrix/client/unstable/org.matrix.msc4143/rtc/transports seems to work (makes sens, as you have to set experimental_features.msc4143_enabled to make it work). It's an authenticated endpoint though, so you have to supply a Bearer token to test it. You can test by doing the following (assuming you are using MAS):

cd /tmp

# Download a script to get tokens via cli
curl -L -O https://raw.githubusercontent.com/element-hq/matrix-authentication-service/refs/heads/main/misc/device-code-grant.sh
chmod +x ./device-code-grant.sh

# Fetch a token
./device-code-grant.sh https://matrix.example.com
# → Follow the procedure, either open a browser or scan the QRCode
# Copy the "access_token" value (only holds a couple of minutes!)

# Test the endpoint:
curl -H 'Authorization: Bearer $mat_your_access_token' https://matrix.example.com/_matrix/client/unstable/org.matrix.msc4143/rtc/transports
# Should return
{"rtc_transports":[{"type":"livekit","livekit_service_url":"https://matrix-rtc.example"}]}

If something is misconfigured, you can use the matrix tester:

# Download the matrix tester
git clone https://codeberg.org/spaetz/testmatrix.git
cd testmatrix
python ./test_matrix.py -u @login:example.com  example.com  -t $mat_your_access_token

Hope this helps!