How to get specific data from external API in ASP.Net

Question

I am trying to fetch the holiday data from an external API in asp.net. The fetch works, but I'd like to use it as a reference on the annual date.

cspublic string Get()
        {
            HttpClient http = new HttpClient();
            http.DefaultRequestHeaders.Add("APIKey", "Application/Json");
            var data = http.GetAsync(url).Result.Content.ReadAsStringAsync().Result;
            return data;
        }

i have this code in my repository file to get external api

i want to get is_national_holiday == true

https://api-harilibur.vercel.app/api

[
  {
    "holiday_date": "2021-01-1",
    "holiday_name": "Tahun Baru Masehi",
    "is_national_holiday": true
  },
  {
    "holiday_date": "2021-01-12",
    "holiday_name": "Hari Siwa Ratri",
    "is_national_holiday": false
  },
  {
    "holiday_date": "2021-01-30",
    "holiday_name": "Hari Saraswati",
    "is_national_holiday": false
  },
  {
    "holiday_date": "2021-02-12",
    "holiday_name": "Tahun Baru Imlek 2572 Kongzili",
    "is_national_holiday": true
  }
]

Update :

Repository

public async Task<HoliDate> GetHolidaysAsync()
        {
            var client = new RestClient($"https://api-harilibur.vercel.app/api");
            var request = new RestRequest(Method.GET);
            IRestResponse response = await client.ExecuteAsync(request);
            if (response.IsSuccessful)
            {
                var content = JsonConvert.DeserializeObject<JToken>(response.Content);

           
                var holidayCaption = content["holiday_date"].Value<DateTime>();

                var holidays = content.SelectTokens("aa")
                     .Select(team => new Holiday
                     {
                         holiday_date = (DateTime)team["holiday_date"],
                         holiday_name = (string)team["holiday_name"],
                         is_national_holiday = (bool)team["is_national_holiday"]
                     })
                    .ToList();

                //return the model to my caller.
                return new HoliDate
                {
                    HolidayCaption = holidayCaption,
                    Holiday = holidays
                };                

            }
            Console.WriteLine(response.Content);

            return null;
        }

Controller

[Route("Holiday")]
        [HttpGet]
        public async Task<IActionResult> GetByIdAsync() { 
        var model = await repository.GetHolidaysAsync();

        if (model == null)
            return NotFound(); 

        return Ok(model);
        }

Model Holiday

public class HoliDate
    {   
        public DateTime HolidayCaption { get; set; }
   
        public IEnumerable<Holiday> Holiday { get; set; }
    }
}

An unhandled exception occurred while processing the request. ArgumentException: Accessed JArray values with invalid key value: "HolidayCaption". Int32 array index expected. Newtonsoft.Json.Linq.JArray.get_Item(object key) LeaveAPI.Repository.Data.LeaveDetailRepository.GetHolidaysAsync() in LeaveDetailRepository.cs + var holidayCaption = content["HolidayCaption"].Value(); LeaveAPI.Controllers.LeaveDetailsController.GetByIdAsync() in LeaveDetailsController.cs + var model = await repository.GetHolidaysAsync();

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