POST API Requests Return 204 Success But Don't Execute Commands on Client Devices

[Calmantras]

Trying to get this to work. Can someone please share some insigth on working with the api to control client playback. Sending messages to the client would be also really nice.

Description of the bug
POST requests to Jellyfin's API endpoints for remote control commands (mute/unmute, pause/play/seek, display messages) return HTTP 204 Success responses but do not produce any visible effects on client devices. GET requests work perfectly, indicating network connectivity and authentication are functioning correctly.

Reproduction steps

1. Set up Jellyfin 10.10.7 in Docker container on Proxmox VM
2. Connect various clients (Windows desktop app, browser client, Android app, iPad app)
3. Obtain valid SessionId from active client sessions
4. Send POST requests to the following endpoints:
   • POST /Sessions/{sessionId}/Command/{command} (for mute/unmute)
   • POST /Sessions/{sessionId}/Playing/{command} (for pause/seek/play)
   • POST /Sessions/{sessionId}/Message (for display messages)
5. Observe that requests return 204 Success but no action occurs on clients

What is the current bug behavior?

• All POST requests return HTTP 204 Success
• No visible response or action occurs on any client device
• Commands are not executed despite successful API response
• Invalid SessionIds are properly logged (confirming requests reach the server)
• Valid SessionIds produce no client-side effects

What is the expected correct behavior?
POST requests should execute the requested commands on the target client devices (mute/unmute audio, pause/play/seek media, display messages on screen).

Jellyfin Server version
10.10.7

Specify version number
10.10.7

Specify the build version
10.10.7

Environment

- OS: Docker container on Proxmox VM
- Virtualization: YES (Proxmox)
- Docker: YES
- Plugins: None specified

Jellyfin logs

Invalid SessionIds are properly logged, confirming requests reach the server.
Valid SessionIds produce no error logs but no client-side effects occur.

Client / Browser logs
Tested on multiple client types:

• Windows desktop app
• Browser client
• Android app
• iPad app

Some clients show "SupportsRemoteControl": true and "SupportsMediaControl": true in their session info, others don't.

Additional information

• Using API documentation from https://api.jellyfin.org/ (version 10.11 docs)
• Network connectivity appears fine (GET requests work, POST returns 204)
• Tested both via external domain and internally within the network
• Tested with various valid SessionIds
• Question: Is this API intended for internal use only, not external extensions?
• Question: Does the Docker deployment affect API functionality differently?

[shamoon]

Ah, I just found your post—I have a similar question in #15857

Did you ever make any progress here?