{
  "endpoint": "recordInvoicePayment",
  "description": "Ohne Idempotenz-Schluessel — eine Wiederholung wuerde zweimal buchen",
  "request": {
    "invoiceId": "invoice_example",
    "method": "transfer",
    "amountCents": 12000
  },
  "expected": {
    "ok": false,
    "code": "validation",
    "fields": [
      "idempotencyKey"
    ]
  }
}