> ## Documentation Index
> Fetch the complete documentation index at: https://manifest.build/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# M001: Missing Authorization header

> Manifest error M001 fires when /v1/chat/completions is called without an Authorization header. Returns HTTP 401. Fix: send `Authorization: Bearer mnfst_<key>`.

## What you saw

```text theme={"theme":{"light":"github-light","dark":"github-dark"}}
[🦚 Manifest M001] Missing the Authorization header. Set it to "Bearer mnfst_<your-key>".
See https://manifest.build/docs/errors/M001
```

## Why it happened

Your client called `/v1/chat/completions` without an `Authorization` header. Manifest checks an agent API key on every request, so the header has to be there.

## How to fix it

1. Grab your agent's key from the [dashboard](https://app.manifest.build) (Workspace, agent, key).
2. Add the header to every request: `Authorization: Bearer mnfst_<your-key>`.
3. If you're using an SDK, set the API key in its config instead of building the header by hand.

## Related

* [M002: Empty Bearer token](/errors/M002)
* [M003: Invalid key format](/errors/M003)
* [M004: Key expired](/errors/M004)
* [M005: Key not recognized](/errors/M005)
* [All error codes](/errors)