Как сделать Post запрос?

Dim postData As String = ("&organizationId=d8d38565926f&customerId=" & ClientIdTxt.Text & "&walletId=fb68-11e7-80cb-d8d385655247&sum=" & SummTxt.Text)
            Dim encoding As New UTF8Encoding
            Dim byteData As Byte() = encoding.GetBytes(postData)
 
            Dim Request As HttpWebRequest = DirectCast(HttpWebRequest.Create("https://iiko.biz:9900/api/0/customers/refill_balance?&access_token=" & token), HttpWebRequest)
            Request.Method = "POST"
            Request.KeepAlive = True
            Request.Proxy = Nothing
            Request.UserAgent = "Firefox/14.0.1"
            Request.ContentLength = byteData.Length
 
            Dim Response As HttpWebResponse = Request.GetResponse
            Dim ResponseStream As Stream = Response.GetResponseStream
 
            Dim StreamReader As New StreamReader(ResponseStream)
            Dim Data As String = StreamReader.ReadToEnd
            StreamReader.Close()
 
            Dim n As Api = JsonConvert.DeserializeObject(Of Api)(Data)
            ClientIdTxt.Text = n.ClientId
            urlResponseTxt.Text = Data

    Friend Function PostRequest() As Boolean
        Dim postData As String = "organizationId=d8d38565926f&customerId=" & ClientIdTxt.Text & "&walletId=fb68-11e7-80cb-d8d385655247&sum=" & SummTxt.Text
        Dim encoding As New UTF8Encoding
        Dim byteData As Byte() = encoding.GetBytes(postData)
        Dim postZapros As HttpWebRequest = DirectCast(WebRequest.Create("https://iiko.biz:9900/api/0/customers/refill_balance?&access_token=" & token), HttpWebRequest)
        postZapros.Method = "POST"
        postZapros.KeepAlive = True
        postZapros.ContentLength = byteData.Length
 
        Try
            Dim postZaprosstream As Stream = postZapros.GetRequestStream()
            postZaprosstream.Write(byteData, 0, byteData.Length)
            postZaprosstream.Close()
            Dim postZaprosOtvetServera As HttpWebResponse = Nothing
            postZaprosOtvetServera = DirectCast(postZapros.GetResponse(), HttpWebResponse)
            Dim postZaprosreader As New StreamReader(postZaprosOtvetServera.GetResponseStream, System.Text.Encoding.UTF8)
            Dim thepage As String = postZaprosreader.ReadToEnd 'Тут ответ
            postZaprosOtvetServera.Close()
            postZaprosreader.Close()
            Return True
        Catch ex As WebException
            Return False
        End Try
    End Function

postZapros.KeepAlive = False