Skip to content
Agent Month
Email

How to fix: 401 authentication error / invalid API key

Last verified: June 2026· All LLM providers

Where this shows up

All LLM providers

The fix

  1. 1Confirm the key is set in the environment and loaded — not hardcoded, not an empty string.
  2. 2Check you’re not setting two conflicting credentials at once (e.g. both an API key and an auth token) — some SDKs send both and the API rejects it.
  3. 3For OAuth/bearer tokens, send them in the Authorization: Bearer header, not the API-key header.
  4. 4Verify the key hasn’t been revoked and has access to the model/workspace you’re calling.
  5. 5Rotate the key if it may have leaked, and move it into a secrets manager.

Prevent it

Load keys from a secrets manager, never commit them, and scope keys narrowly per service.

Common variations and related errors

You'll usually hit this same root cause under a few different names. Same fix.

  • "401 unauthorized"
  • "invalid API key"
  • "Incorrect API key provided"
  • "Authentication credentials not found"
  • "expired token"
  • "invalid_api_key"

Frequently asked questions

What causes “401 authentication error / invalid API key”?

The API key is missing, malformed, revoked, or sent the wrong way (e.g. an OAuth token in the API-key header).

How do I prevent “401 authentication error / invalid API key” from recurring?

Load keys from a secrets manager, never commit them, and scope keys narrowly per service.