Error updating MCP custom user variables {{0}}

[mboret]

What happened?

Hi,

I'm trying to define a custom env variable to connect to an MCP server. Still, when I define the required MCP variable and click the 'save' button, I get "Error updating MCP custom user variables {{0}}".

I tried with the documentation example, but I get the same error:

mcpServers:
  MCPServer1:
    type: streamable-http
    url: http://host.docker.internal:4000/mcp
    headers:
      X-Auth-Token: "{{MY_SERVICE_API_KEY}}"
    customUserVars:
      MY_SERVICE_API_KEY:
        title: "My Service API Key"
        description: "Enter your personal API key for the service. You can generate one at <a href='https://myservice.example.com/developer/keys' target='_blank'>Service Developer Portal</a>."
    timeout: 30000
    serverInstructions: false

Version Information

110984b

Steps to Reproduce

1. Add a custom MCP user env variable in librechat.yaml
2. Set a value, for this variable in the UI

What browsers are you seeing the problem on?

Firefox

Relevant log output

LibreChat         | 2025-07-11 06:37:48 error: [updateUserPluginAuth] Invalid key length
LibreChat         | 2025-07-11 06:37:48 error: [authService] Invalid key length
LibreChat         | 2025-07-11 06:37:48 error: [updateUserPluginsController] Invalid status code: undefined

Screenshots

No response

Code of Conduct

• I agree to follow this project's Code of Conduct

[danny-avila]

Make sure you set CREDS_KEY and CREDS_IV values in the your .env file.

https://www.librechat.ai/toolkit/creds_generator

There are also default examples in .env.example, however, it's recommended you generate your own.

[mboret]

Thanks for your answer @danny-avila . You're right, I no longer encounter the error after setting the key (MCP Custom user env variables updated successfully). The logs also show:

LibreChat | 2025-07-11 07:43:40 info: [updateUserPluginsController] Disconnecting MCP connections for user 686ccf9de5c30b342859180d after plugin auth update for mcp_MCPServer1.