ChallengedUri выдал исключение

Основной код:

var request = (HttpWebRequest)WebRequest.Create("https://tele2.ru/api/subscribers/номер_телефона/rests");//status=connected
request.CookieContainer = new CookieContainer();
request.CookieContainer.Add(new Uri("https://login.tele2.ru/ssotele2/wap/auth"), cook);
request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8";
request.UserAgent = "Mozilla/5.0 (Windows NT 6.3; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36";
request.ContentType = "application/json;charset=utf-8";
request.KeepAlive = true;
request.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;
request.Headers.Add("DNT", "1");
request.Method = "GET";
request.AllowAutoRedirect = false;
using (var response = (HttpWebResponse)await request.GetResponseAsync())
{
    using (var read = new StreamReader(response.GetResponseStream()))
    {
        var result = await read.ReadToEndAsync();
    }
}

Исключение выдает здесь:

using (var response = (HttpWebResponse)await request.GetResponseAsync())

Вопрос: из-за чего это возникает? Как исправить? Подскажите, пожалуйста.

Убрал блок try{} catch{}: