I am using Codex CLI on Windows -- latest version

codex-cli 0.140.0-alpha.2

I follow the Codex/MCP/OAuth instructions here: https://dashboard.composio.dev/olmstead/~/connect/clients/codex

codex mcp list

shows:

Name      Url                               Bearer Token Env Var  Status   Auth
composio  https://connect.composio.dev/mcp  -                     enabled  OAuth

Launching

codex

yields this:

⚠ MCP client for `composio` failed to start: MCP startup failed: handshaking with MCP server failed: Send message error
  Transport
  [rmcp::transport::worker::WorkerTransport<rmcp::transport::streamable_http_client::StreamableHttpClientWorker<rmcp::tr
  ansport::auth::AuthClient<codex_rmcp_client::http_client_adapter::StreamableHttpClientAdapter>>>] error: Auth error:
  OAuth authorization required, when send initialize request

⚠ MCP startup incomplete (failed: composio)

How can this be resolved?

Hi there, That error is the OAuth authorization step not completing.

codex mcp add

only registers the server (which is why it shows up in

codex mcp list

), but you still need the separate login step to authorize it:

codex mcp login composio

Complete the browser sign-in, then relaunch

codex

and the handshake should go through. If you already ran that and it still fails, the OAuth loopback callback can get blocked on Windows. Two options: • Run

codex mcp logout composio

, then retry the login in your default browser signed into a single Composio account. • Or switch to the API Key method, which skips the browser flow entirely and tends to be more reliable on Windows. Open the API Key tab on the same Codex setup page (https://dashboard.composio.dev/olmstead/~/connect/clients/codex); it gives you the exact

~/.codex/config.toml

block with your key already filled into the

x-consumer-api-key

header. Use that key as-is (not a project API key, and not an Authorization header). Just reply here with a fresh error if it's still off after that. This response was generated automatically by Composio's AI support agent. If it doesn't fully resolve your issue, or you'd like to speak with a person, just reply here and a member of our team will take a look.