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401
Client Error

401 Unauthorized

Authentication is required and has failed or not been provided.

Definition (RFC 9110)

HTTP status code 401 401 Unauthorized is defined in RFC 9110 (HTTP Semantics), Section 15.5.2 — the current authoritative specification for HTTP semantics, published June 2022, which obsoletes the older RFC 7231 and RFC 2616.

Description

The 401 Unauthorized status code indicates that the request has not been applied because it lacks valid authentication credentials. The response must include a WWW-Authenticate header indicating the authentication scheme.

Common Causes

  • Missing or expired authentication token
  • Invalid API key
  • Session expired
  • Incorrect username or password

How to Fix

  • Include valid credentials in the request
  • Refresh expired tokens
  • Check API key validity
  • Re-authenticate if session expired

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Related Status Codes

400
400 Bad Request
The server cannot process the request due to malformed syntax.
 402
402 Payment Required
402 Payment Required — code reserved for future use, but currently used by some APIs to signal "payment needed".
 403
403 Forbidden
The server understood the request but refuses to authorize it.
 404
404 Not Found
404 Not Found — the requested URL does not exist on the server. The most common client-error; signals search engines to remove the page from index.
 405
405 Method Not Allowed
The HTTP method used is not allowed for this resource.
 406
406 Not Acceptable
The server cannot produce a response matching the client's Accept headers.

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