{
  "type": "function",
  "function": {
    "name": "modify_reservation",
    "description": "Modify an existing reservation",
    "parameters": {
      "type": "object",
      "properties": {
        "user_id": {
          "type": "string",
          "description": "User ID"
        },
        "reservation_id": {
          "type": "string",
          "description": "Reservation ID to modify"
        },
        "modification_type": {
          "type": "string",
          "enum": ["change_flights", "change_cabin", "add_bags", "update_passenger"],
          "description": "Type of modification"
        },
        "new_details": {
          "type": "object",
          "description": "New details for the modification"
        },
        "payment_method": {
          "type": "string",
          "description": "Payment method for additional charges"
        }
      },
      "required": ["user_id", "reservation_id", "modification_type"]
    }
  }
}