Element Call fails with OPEN_ID_ERROR but no OpenID request is sent

[choa1111]

Steps to reproduce

1. Use a self-hosted Synapse homeserver.
2. Upgrade the homeserver from Synapse 1.136 to Synapse 1.151.
3. Configure MatrixRTC / Element Call with a separate LiveKit server and lk-jwt-service.
4. Configure MatrixRTC discovery through both:
   • /.well-known/matrix/client
   • Synapse matrix_rtc.transports
5. Confirm that desktop web clients can use Element Call successfully.
6. Confirm that a mobile browser using the self-hosted Element Call frontend can also use the same Element Call / LiveKit deployment successfully.
7. On Element X Android, log in with an affected account on the same homeserver.
8. Open a room and start or join an Element Call.
9. Element X Android fails with OPEN_ID_ERROR, or enters the call screen but stays stuck on Waiting for media.
10. Check the homeserver reverse proxy logs during the failing attempt.

Observed server-side behavior

During the failing Element X Android attempt, the client still contacts the homeserver normally.

The homeserver receives requests such as:

• GET /.well-known/matrix/client
• GET /_matrix/client/v3/profile/...
• GET /_matrix/client/v3/rooms/.../members
• POST /_matrix/client/unstable/org.matrix.simplified_msc3575/sync
• other normal sync/profile/member requests

However, during the failing Element X Android attempt, the homeserver does not receive this request:

• POST /_matrix/client/v3/user/{userId}/openid/request_token

The homeserver also does not receive the expected MatrixRTC call membership event from the failing Android client.

By contrast, when the same call is joined from desktop web or from the mobile browser Element Call frontend:

• the OpenID request is sent successfully
• the JWT service validates it successfully
• the MatrixRTC call membership event is sent
• the call works

Observed client-side behavior

Element X Android shows either:

• OPEN_ID_ERROR
• or Waiting for media

Relevant Element X log messages include:

• [ElementCall] [LocalTransport] Failed to authenticate to transport ... {"code":"OPEN_ID_ERROR"}
• [CallViewModel][LocalMembership] Multiple Transport Errors
• Uncaught Error: Something went wrong

Important detail

The error shown in the UI is OPEN_ID_ERROR, but based on homeserver access logs, the OpenID request is not failing on the server side.

It appears that Element X Android never sends the OpenID token request at all during the failing attempt.

This makes me suspect the issue may be in the Element X Android / embedded Element Call / WebView OpenID bridge path, rather than in the Synapse OpenID endpoint itself.

Outcome

What did you expect?

Element X Android should request an OpenID token from the homeserver by calling:

POST /_matrix/client/v3/user/{userId}/openid/request_token

Then it should pass the OpenID token to the configured LiveKit JWT service, receive LiveKit credentials, publish the MatrixRTC call membership event, and join the Element Call successfully.

What happened instead?

Element X Android fails with OPEN_ID_ERROR or gets stuck on Waiting for media.

The homeserver logs show that the OpenID request is not sent by Element X Android during the failing attempt.

Desktop web clients and the mobile browser Element Call frontend can use the same homeserver, same room, same LiveKit server, and same JWT service successfully.

Additional context

• The issue started after upgrading Synapse from 1.136 to 1.151.
• The reverse proxy was also upgraded around the same time.
• The current MatrixRTC / LiveKit setup works from web clients.
• The Synapse OpenID endpoint works when used by desktop web Element Call.
• The LiveKit JWT service works when used by desktop web Element Call.
• The problem appears to be specific to Element X Android for some accounts/sessions.
• Clearing cache did not fix the issue.
• The issue reproduces on both Element X Android 26.06.4 and 26.05.2.
• A mobile browser on the same phone can use the self-hosted Element Call frontend successfully.

Your phone model

Samsung S23 / Samsung S23+

Operating system version

Android 16

Application version and app store

Element X Android 26.06.4

Homeserver

Self-hosted Synapse 1.151 The homeserver was upgraded from Synapse 1.136. MatrixRTC / MSC4143 is enabled. Element Call is configured with a separate LiveKit server and lk-jwt-service.

Will you send logs?

Yes

Are you willing to provide a PR?

No

[choa1111]

##This is more imformation

Summary

Element X Android fails to join Element Call / MatrixRTC calls on my self-hosted Synapse + LiveKit setup.

The call UI opens, but the client shows OPEN_ID_ERROR or gets stuck on Waiting for media.

Server logs show that, in the failing Element X path, the client does not send an OpenID token request at all.

The same account can use Element Call successfully from desktop/web clients and from a mobile browser using the self-hosted Element Call frontend.

Environment

Homeserver:

• Synapse upgraded from 1.136 to 1.151
• Server name: example.org
• Reverse proxy: nginx 1.30
• Element Call / LiveKit hosted separately at https://rtc.example.org
• LiveKit JWT service URL: https://rtc.example.org/livekit/jwt
• LiveKit SFU URL used by lk-jwt-service: wss://rtc.example.org/livekit/sfu

Android client:

• Device: Samsung S23 / SC-51D
• Android: 16
• Element X Android tested versions:
  • 26.06.4
  • 26.05.2

Synapse MatrixRTC configuration

experimental_features:
  msc3266_enabled: true
  msc4222_enabled: true
  msc4140_enabled: true
  msc4143_enabled: true

max_event_delay_duration: 24h

rc_message:
  per_second: 0.5
  burst_count: 30

rc_delayed_event_mgmt:
  per_second: 1
  burst_count: 20

matrix_rtc:
  transports:
    - type: livekit
      livekit_service_url: "https://rtc.example.org/livekit/jwt"

extra_well_known_client_content:
  "org.matrix.msc4143.rtc_foci":
    - type: "livekit"
      livekit_service_url: "https://rtc.example.org/livekit/jwt"

Well-known response

GET /.well-known/matrix/client returns:

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

Expected behavior

Element X should request an OpenID token from Synapse, authenticate to the LiveKit JWT service, write the call membership event, and join the call.

Expected Matrix request:

POST /_matrix/client/v3/user/@user:example.org/openid/request_token

Expected call membership request:

PUT /_matrix/client/v3/rooms/<room_id>/state/org.matrix.msc3401.call.member/...

Actual behavior

Element X opens the call UI but fails with:

OPEN_ID_ERROR

or remains stuck on:

Waiting for media

Element X logs include:

[ElementCall] [LocalTransport] Failed to authenticate to transport https://rtc.example.org/livekit/jwt
{"localisedTitle":"Something went wrong","category":"CONFIGURATION_ISSUE","code":"OPEN_ID_ERROR"}

[ElementCall] [CallViewModel][...][LocalMembership] Multiple Transport Errors:
{"localisedTitle":"Something went wrong","category":"CONFIGURATION_ISSUE","code":"OPEN_ID_ERROR"}

[ElementCall] https://appassets.androidplatform.net/element-call/assets/index-....js:277
Uncaught (in promise) Error: Something went wrong

In another failing attempt, before the OpenID error:

[ElementCall] [CallViewModel][...][LocalMembership] Failed to send join action {}
[ElementCall] Error calling setAlwaysOnScreen(true) {}

Server-side observation

During failing Element X attempts, nginx/Synapse logs show Element X requests like:

GET /.well-known/matrix/client 200
GET /_matrix/client/v3/profile/@user:example.org 200
GET /_matrix/client/v3/rooms/<room_id>/members 200
POST /_matrix/client/unstable/org.matrix.simplified_msc3575/sync 200

But there is no request for:

POST /_matrix/client/v3/user/@user:example.org/openid/request_token

And no request for:

PUT /_matrix/client/v3/rooms/<room_id>/state/org.matrix.msc3401.call.member/...

So the failure appears to happen before the Matrix SDK sends the OpenID request.

Things already tested

• Desktop/web Element Call works.
• Mobile browser using the self-hosted Element Call frontend works.
• The same homeserver OpenID endpoint works when requested by web clients.
• LiveKit JWT service works for web clients.
• LIVEKIT_URL in lk-jwt-service is set to the SFU WebSocket URL:
  wss://rtc.example.org/livekit/sfu
• livekit_service_url in Synapse and well-known is:
  https://rtc.example.org/livekit/jwt
• Temporarily disabled matrix_rtc.transports to force discovery via /.well-known/matrix/client; Element X still failed.
• Cleared app cache / tested different Element X versions.
• Tested Element X 26.06.4 and 26.05.2.

Question

Why would Element X show OPEN_ID_ERROR without sending /_matrix/client/v3/user/.../openid/request_token at all?

Is there a known issue in the Element Call WebView / widget bridge / OpenID bridge path on Android, especially with self-hosted Synapse 1.140+ MatrixRTC deployments?

What additional logs would be useful to debug the WebView-to-native OpenID bridge?