Idempotency payload mismatch

What it means

The Idempotency-Key was already used with a different request body.

Common causes

• A key was reused for a different write.
• The body changed between retries, for example a fresh timestamp field.

What to do

Use a new key for a new write. When you retry, send exactly the same body as the first attempt.

Retry: only after a fix. The same request fails the same way until you change the request, the credential or the resource.

Over MCP, the same failure is a tool result with isError: true, the code idempotency_payload_mismatch and retryable: false.

Example

A response body for this problem. The detail and instance vary with the request.

{
  "type": "https://api.tobie.team/problems/idempotency_payload_mismatch",
  "title": "Idempotency payload mismatch",
  "status": 422,
  "detail": "This Idempotency-Key was used with a different payload",
  "code": "idempotency_payload_mismatch",
  "instance": "/v1/tasks",
  "requestId": "01JC0S7Z5F3X9QK2M4N6P8R0TV"
}