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

# M003: Invalid key format

> M003 is returned when the Bearer token does not start with mnfst_. Use a harness key, not a provider key.

## What you saw

```text theme={"theme":{"light":"github-light","dark":"github-dark"}}
[🦚 Manifest M003] That doesn't look right. Manifest keys start with "mnfst_". Grab yours from the dashboard.
See https://manifest.build/llm-gateway/docs/errors/M003
```

## Why it happened

harness keys always start with `mnfst_`. Your token has a different prefix, which almost always means a provider key (OpenAI, Anthropic, etc.) got pasted into the wrong field.

## How to fix it

1. Open the [dashboard](https://app.manifest.build) and copy your harness's key. It looks like `mnfst_xxxxxxxxxxxx`.
2. Replace the token in your client's config and retry.
3. Provider keys (OpenAI's `sk-...`, etc.) belong on the **Routing** page, not in the Authorization header.

## Related

* [M001: Missing Authorization header](/llm-gateway/docs/llm-gateway/docs/errors/M001)
* [M005: Key not recognized](/llm-gateway/docs/llm-gateway/docs/errors/M005)
* [M100: Provider API key missing](/llm-gateway/docs/llm-gateway/docs/errors/M100)
* [API key providers](/llm-gateway/docs/llm-gateway/docs/providers/api-key-providers)
* [All error codes](/llm-gateway/docs/llm-gateway/docs/errors)