{
  "type": "object",
  "properties": {
    "client_id": {
      "type": "string",
      "description": "Client number"
    },
    "customer_number": {
      "type": "string", 
      "description": "Customer number"
    },
    "level": {
      "type": "integer",
      "enum": [1, 2, 3],
      "description": "Dunning level"
    },
    "invoice_numbers": {
      "type": "array",
      "description": "Outstanding invoice numbers"
    },
    "amount": {
      "type": "number",
      "description": "Total amount"
    },
    "fee": {
      "type": "number",
      "description": "Dunning fee"
    },
    "deadline": {
      "type": "string",
      "format": "date",
      "description": "Payment deadline"
    }
  },
  "required": ["client_id", "customer_number", "level", "invoice_numbers"]
}