Разбор JSON с сайта случайных ошибок с 500

Question

Я создал приложение, которое подключается к внешнему веб-сайту (вне моего контроля) к сервису мониторинга, который мы купили. Веб-сайт в основном представляет собой веб-API с графическим интерфейсом для машин, подобных поставщикам.

Из-за некоторых вещей я хотел сделать оповещения SMTP, если что-то пошло не так, поскольку наш поставщик еще не создал такую ​​функциональность.

Мой код работает с HttpWebRequest, и мое приложение открывает сайт, выполняет вход, успешно перенаправляет. Но когда я вызываю POST, это дает мне 500 ошибок HTTP в основном. Ошибка совершенно случайна, потому что иногда все может быть успешным и работать совершенно нормально, и просто через несколько минут не работает.

Часть моего кода:

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12
Dim request As HttpWebRequest = CType(HttpWebRequest.Create("https://website.com"), HttpWebRequest)
Dim cookieContainer = New CookieContainer()
    request.CookieContainer = cookieContainer
    request.UserAgent = "Mozilla/5.0 (Windows NT 10.0 WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.101 Safari/537.36"
    request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"
    request.AutomaticDecompression = DecompressionMethods.Deflate Or DecompressionMethods.GZip
    request.Host = "xxx"
    request.Headers.Add("DNT", "1")

    Dim Fullhtmlcode As String

    Using response As WebResponse = request.GetResponse()
        Using sr As New StreamReader(response.GetResponseStream())
            Fullhtmlcode = sr.ReadToEnd
        End Using
    End Using

    Dim SearchingString As String = "somestring"
    Dim SearchingStringIndexINt As Integer = Fullhtmlcode.IndexOf(SearchingString)
    Dim length As Integer = SearchingString.Length
    Dim TokenArr() As Char = Fullhtmlcode.ToCharArray(SearchingStringIndexINt + length, 40)
    Dim TokenString As String = New String(TokenArr)

    request = TryCast(WebRequest.Create("https://website.com"), HttpWebRequest)
    request.KeepAlive = True
    request.CookieContainer = cookieContainer
    request.Headers.Add("DNT", "1")
    request.UserAgent = "Mozilla/5.0 (Windows NT 10.0 WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.101 Safari/537.36"
    request.Accept = "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8"
    request.Method = "POST"
    request.ContentType = "application/x-www-form-urlencoded"
    request.KeepAlive = True
    request.AllowAutoRedirect = True
    request.AutomaticDecompression = DecompressionMethods.Deflate Or DecompressionMethods.GZip

    Dim Data As String = ("_token=" + TokenString + "&login=login&password=password")
    Dim bytes As Byte() = UTF8Encoding.UTF8.GetBytes(Data)
    request.ContentLength = bytes.Length

    'login in
    Using dataStream As Stream = request.GetRequestStream()
        dataStream.Write(bytes, 0, bytes.Length)
        dataStream.Close()
    End Using

    Using response As WebResponse = request.GetResponse()
        Using sr As StreamReader = New StreamReader(response.GetResponseStream())
            'Console.WriteLine(sr.ReadToEnd())
        End Using
    End Using

    'get json data
    Try
        Dim requester As HttpWebRequest = CType(HttpWebRequest.Create("https://website.com/ajax/getMachines"), HttpWebRequest)


        requester.Method = "POST"
        requester.Host = "website.com"
        requester.UserAgent = "Mozilla/5.0 (Windows NT 10.0 WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/45.0.2454.101 Safari/537.36"
        requester.Accept = "application/json, text/plain, */*"
        requester.AutomaticDecompression = DecompressionMethods.Deflate Or DecompressionMethods.GZip
        requester.ContentType = "application/json;charset=utf-8"
        requester.KeepAlive = True
        requester.CookieContainer = cookieContainer
        requester.Referer = "https://website.com/"

        Dim Uri = New Uri("https://website.com/ajax/getMachines")
        'adding X-XSRF-TOKEN
        For Each coookie In cookieContainer.GetCookies(Uri)
            If coookie.ToString().Contains("XSRF-TOKEN") Then
                Dim CookieLenght As Integer = coookie.ToString().Length
                Dim c() As Char = coookie.ToString().ToCharArray(11, CookieLenght - 11)
                Dim d As String = New String(c)
                requester.Headers.Add("X-XSRF-TOKEN", c)
                requester.Headers.Add("DNT", "1")
            End If
        Next

        Data = "json data"
        requester.ContentLength = Data.Length
        bytes = UTF8Encoding.UTF8.GetBytes(Data)
        requester.ContentLength = bytes.Length

        Using dataStream As Stream = requester.GetRequestStream() 'calling json 
            dataStream.Write(bytes, 0, bytes.Length)
            dataStream.Close()
        End Using

        Using responser As WebResponse = requester.GetResponse()   'random error 500
            Using sr As StreamReader = New StreamReader(responser.GetResponseStream())
                Console.WriteLine(sr.ReadToEnd())
            End Using
        End Using
    Catch ex As Exception
        Console.WriteLine(ex.ToString)
    End Try