idempotency_conflict — HTTP 409

Idempotency-Key reused with a different body, or a request with that key is still in flight.

Example response

{
  "ok": false,
  "request_id": "req_...",
  "error": {
    "code": "idempotency_conflict",
    "message": "Idempotency-Key reused with a different body, or a request with that key is still in flight."
  }
}

Why it happens

• An `Idempotency-Key` header was reused with a different request body.
• A request with the same key is still in flight (e.g. a client retried before the first attempt finished).

How to fix it

• Generate a fresh key (UUID) per logical request; reuse a key only to retry the exact same body.
• If the first request is still running, wait for it to settle instead of firing a duplicate.