Manifest error codes

When Manifest blocks or rejects a request, the response message starts with a code in square brackets:

[🦚 Manifest M100] No anthropic API key yet. Add one here: https://app.manifest.build/...
See https://manifest.build/docs/errors/M100

Look up the code below to see what it means and how to fix it.

Authentication (M001–M005)

These fire when the bearer token on /v1/chat/completions is missing or wrong. They surface as HTTP 401 to non-chat clients.

Code	What
M001: Missing Authorization header	No `Authorization` header on the request
M002: Empty Bearer token	Header present, token after `Bearer` is blank
M003: Invalid key format	Token doesn’t start with `mnfst_`
M004: Key expired	Key past its expiration date
M005: Key not recognized	No matching agent for this key

Your key is fine, but no provider credentials are wired up. See Routing and API key providers.

Code	What
M100: Provider API key missing	Routing picked a provider you haven’t connected
M101: No providers configured	Agent has zero providers connected

You hit a usage cap or rate limit. They surface as HTTP 429. See Set limits.

Code	What
M200: Usage limit exceeded	Cost or message-count limit you set was crossed
M201: Per-user rate limit exceeded	More than 200 requests/minute from one user
M202: Per-IP rate limit exceeded	More than 500 requests/minute from one IP
M203: Concurrency limit exceeded	More than 10 in-flight requests at once

The request body is malformed. They surface as HTTP 400.

Code	What
M300: Missing messages array	Body has no `messages` array, or it’s empty
M301: Messages array too long	More than 1000 messages in a single request

Manifest itself broke. Surfaces as HTTP 500.

Code	What
M500: Internal server error	Unhandled error in the proxy pipeline