{
  "endpoint": "issueInvoice",
  "description": "Die Nummer vergibt der Server",
  "request": {
    "idempotencyKey": "ex-8",
    "customerId": "customer_example",
    "taxScheme": "normal",
    "priceMode": "net",
    "serviceStart": "2026-09-14",
    "items": [
      {
        "description": "Beratung",
        "quantity": 1,
        "unitPriceCents": 5000,
        "vatRate": 20
      }
    ],
    "number": "2026-0001"
  },
  "expected": {
    "ok": false,
    "code": "validation",
    "fields": [
      "number"
    ]
  }
}