# What does the VARTA error `idempotency_key_reuse` mean?

The `Idempotency-Key` you sent was already used, with a different request body.


**HTTP status:** `409`  ·  **Type:** `invalid_request_error`

## What it means

The `Idempotency-Key` you sent was already used, with a different request body.

## What causes it

The idempotency layer fingerprints method, path and body per key; a stored fingerprint that doesn't match the current request raises this (`backend/app/api/v1/idempotency.py`).

## What to do

Generate a new key per logically distinct request. Never reuse one key across two different request bodies.