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405 Method Not Allowed

The HTTP method (GET, POST, PUT, DELETE) is not supported for this endpoint.

Common Causes

  1. 1Using POST on a GET-only endpoint
  2. 2API doesn't support the DELETE method
  3. 3Wrong HTTP verb in the request
  4. 4CORS preflight OPTIONS request not handled

How to Fix

Handle OPTIONS for CORS preflight

// Next.js API route
export async function OPTIONS() {
  return new Response(null, {
    headers: {
      'Allow': 'GET, POST, OPTIONS',
    },
  });
}

Handle OPTIONS requests for CORS preflight.

How ObserveOne Helps

ObserveOne validates API method support and detects misconfigured endpoints.

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Related Errors

400 Bad Request

The server cannot process the request due to malformed syntax, invalid parameters, or bad encoding.

401 Unauthorized

The request requires authentication. The client must provide valid credentials.

403 Forbidden

The server understood the request but refuses to authorize it. Authentication won't help — the user lacks permissions.

404 Not Found

The server cannot find the requested resource. The URL may be wrong, the resource may have been deleted, or the route doesn't exist.

410 Gone

The resource existed but has been permanently removed. Unlike 404, this explicitly tells clients the resource won't come back.