{
  "type": "object",
  "properties": {
    "customer_id": {
      "type": "string",
      "description": "Customer ID"
    },
    "invoice_date": {
      "type": "string",
      "format": "date",
      "description": "Invoice date"
    },
    "due_date": {
      "type": "string",
      "format": "date",
      "description": "Due date"
    },
    "description": {
      "type": "string",
      "description": "Service description"
    },
    "quantity": {
      "type": "number",
      "description": "Quantity"
    },
    "rate": {
      "type": "number",
      "description": "Unit price"
    }
  },
  "required": ["customer_id", "invoice_date"]
}