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404 Not Found

Use one of the exact built-in paths:
There is no combined /MCP endpoint. Also check URL casing, reverse-proxy path rewriting, and whether the module providing the endpoint started successfully.

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codex mcp login cannot discover OAuth

Open both metadata documents directly:
If either fails, fix the Neuron, TLS certificate, DNS, or proxy before changing Codex configuration.

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Client registration fails

Dynamic registration is optional. Ask the operator whether DCR is enabled and tested. Otherwise remove the MCP entry and add it again with a supplied client ID:

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Login succeeds but requests return 403

The account lacks one or more requested privileges. Compare each requested scope with its role privilege:
After the role changes, log in again so Codex obtains a token with the new scope.

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No tools or resources appear

  • Confirm Codex is connected to the intended specialized endpoint.
  • Run codex mcp list and inspect /mcp inside Codex.
  • Check that the requested leaf scopes include the operation you expect.
  • Check Neuron startup and event logs for module errors.

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Bearer token works only in one terminal

--bearer-token-env-var stores the environment variable’s name, not its value. Define that variable in every process that launches Codex. Do not put the token itself in config.toml.

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Information to collect

Record the endpoint, UTC time, client ID, requested scopes, HTTP status, JSON-RPC error, Neuron version, and event ID. Remove access tokens, refresh tokens, authorization codes, cookies, client secrets, and passwords.