Error code: unknown_field

What triggers it

The body contained a field the endpoint does not accept. A typo in a field name or a field copied from a different endpoint.

Example response

{
  "error": {
    "type": "invalid_request_error",
    "code": "unknown_field",
    "message": "The body contained a field the endpoint does not accept."
  }
}

How to fix it

Remove or correct the field; check the endpoint reference for accepted keys.

This is deterministic: the same request will fail again until fixed. See the HTTP 400 page for the class.

In practice

In a well-built client, unknown_field is handled by branching on error.code rather than on the human error.message, which may be reworded over time. The HTTP status (400) gives the broad invalid_request_error class; the code gives the specifics; and, on field errors, error.param pinpoints the input to fix.

This code is deterministic — retrying the identical request reproduces it — so keep it out of your retry path and instead map it to a clear, actionable message. See Map errors to user-facing messages and Read the error envelope for the pattern.