{
  "endpoint": "issueInvoice",
  "description": "Unbekannte Sprache",
  "request": {
    "idempotencyKey": "ex-en-2",
    "taxScheme": "normal",
    "priceMode": "net",
    "serviceStart": "2026-09-15",
    "language": "fr",
    "items": [
      {
        "description": "Beratung",
        "quantity": 1,
        "unitPriceCents": 1000,
        "vatRate": 20
      }
    ]
  },
  "expected": {
    "ok": false,
    "code": "validation",
    "fields": [
      "language"
    ]
  }
}