> ## Documentation Index
> Fetch the complete documentation index at: https://docs.tryaeris.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Idempotency key reused with different payload (IDEMPOTENCY_CONFLICT)

> The idempotency_key was previously used with a different set of arguments.

## What it means

Aeris remembers every `idempotency_key` it accepts on a mutating tool along with a hash of the payload. If the same key comes back with a **different** payload, that's a client bug — either a stale key was reused across intents, or two different intents accidentally share a key.

This is not retryable with the same key. The client must mint a fresh key.

## How to fix

* Generate a new `idempotency_key` (UUIDv4 recommended) for the new intent.
* Audit how your client scopes keys — keys should be per-intent, not per-session or per-user.
* If you meant to replay the original call, use the original payload with the original key.

## Response envelope

```json theme={"dark"}
{
  "ok": false,
  "error_envelope": {
    "code": "IDEMPOTENCY_CONFLICT",
    "message": "The idempotency_key was previously used with a different payload.",
    "docs_url": "https://tryaeris.ai/docs/mcp/errors/idempotency-conflict",
    "retryable": false,
    "retry_after_ms": null,
    "details": {
      "idempotency_key": "c3f3f0be-4b7a-4e7e-9e5e-8f5a1a7d1b12"
    }
  }
}
```

## Related

* [`IDEMPOTENCY_REQUIRED`](/mcp/errors/idempotency-required) — the key was missing entirely.
* [`CONFLICT`](/mcp/errors/conflict) — also 409, but about resource state, not idempotency bookkeeping.