HTTP 409idempotency

Idempotency-Key conflict

idempotency_conflict

What it means

You sent an `Idempotency-Key` that was used in the last 24 hours with a different request body.

Common causes

Client retried with the same key but the payload changed (different ingredient, dose, region, etc.).
Two parallel processes reused the same idempotency key for different work.

How to fix

Use a fresh key (UUID v4 is conventional) per logical operation.
If you genuinely want to replace the cached response, drop the `Idempotency-Key` header and resubmit.

Example

// First call OK
POST /v1/check  Idempotency-Key: 9c…  body { "ingredient": "vitamin C" }

// Second call — same key, different body → 409
POST /v1/check  Idempotency-Key: 9c…  body { "ingredient": "vitamin D" }