Idempotency key reused

What it means

The Idempotency-Key has been seen before with a *different* body. A repeated key with the same body replays the original response, which is what makes a retry safe; a repeated key with different content is a client bug, and treating it as a replay would silently drop a real second record.

What to do

Generate a key per submission, not per component render or per session.

The response

{
  "type": "https://casanova.realty/problems/idempotency-conflict",
  "title": "Idempotency key reused",
  "status": 409,
  "detail": "A sentence about this particular occurrence.",
  "instance": "/api/v1/properties/some-listing"
}

Content type is application/problem+json. Match on type, not on title — the title is prose and may be rewritten.