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idempotency_key_conflict

409 Conflict   This idempotency key is already in use for a different request.

When you get it

This idempotency key is already in use for a different request. It is always answered with HTTP 409 - one code means one status, so a client may key its handling on either.

Fields it carries

Inside each errors[] entry, beside pointer:

key

The uniqueness key the request collided on.

firstSeenAt

When the server first saw this idempotency key.

reason

The machine-readable sub-case, when one code covers several. Branch on it.

retryAfterSeconds

How long to wait before retrying, in seconds. Mirrors the Retry-After header.

A field is omitted when the server genuinely does not know it - an absent member is never the same as an empty one.

How to fix it

The key you sent is already in use. If `reason` is `different_body`, the same key was reused for a different request - send a fresh key. If `reason` is `in_flight`, the original request is still running: wait for the `Retry-After` interval and retry with the SAME key, which is exactly what the key is for. Do not change the body to work around it.

Shape

{
  "type":   "https://api2.host-tracker.com/problems/idempotency-key-conflict",
  "title":  "This idempotency key is already in use for a different request.",
  "status": 409,
  "code":   "idempotency_key_conflict",
  "errors": [
    { "key": …, "firstSeenAt": …, "reason": …, "retryAfterSeconds": … }
  ]
}