How to upload json data using webclient to a custom class post method in VB.net? - asp.net

Question

I'm trying to upload Json data via WebClient to my web service post method, which is getting the body parameter as custom class variable.
I'm getting 404 error when I post the request. Looking for help to send this post data successfully to my web service.
I tried to send the post request like below
Dim webclient As New WebClient()
Dim reqString As Byte()
Dim resByte As Byte()
Dim sendMessage As Object
sendMessage = New With {Key .chatID = "***********", .messageText = "test"}
webclient.Headers("content-type") = "application/json"
webclient.Headers("accept") = "text/plain"
reqString = Encoding.Default.GetBytes(JsonConvert.SerializeObject(sendMessage))
resByte = webclient.UploadData("http://testurl/SendMessage", "post", reqString)
...
This is my web service method
...
[HttpPost("/SendMessage")]
public string SendMessage([FromBody] SendMessage sendMessage)
{
string apiToken = "*******************************************";
string urlString = "https://api.telegram.org/bot{0}/sendMessage?chat_id={1}&text={2}";
string messageText = sendMessage.messageText;
string chatId = sendMessage.chatID;
urlString = String.Format(urlString, apiToken, chatId, messageText);
try
{
WebRequest request = WebRequest.Create(urlString);
WebResponse response = request.GetResponse();
string responseStatus = ((HttpWebResponse)response).StatusDescription;
if (responseStatus == "OK")
{
using (Stream dataStream = response.GetResponseStream())
{
// Open the stream using a StreamReader for easy access.
using (StreamReader reader = new StreamReader(dataStream))
{
// Read the content.
string responseFromServer = reader.ReadToEnd();
// Check the content.
if (responseFromServer.Contains("\"ok\":true"))
{
// Display a confirmation.
return ("Message text was successfully sent to Telegram :-)");
}
else
{
// Display an error.
return ("Failed to send the message text to Telegram :-(");
}
// Display the content.
return (responseFromServer);
}
}
}
else
{
// Display an error.
return ("Failed to send the message text to Telegram :-(");
return ("Response status: " + responseStatus);
}
// Close the response.
response.Close();
//Console.ReadKey();
}
catch (Exception ex)
{
// Display an error.
return ("Failed to send the message text to Telegram :-(");
return (ex.ToString());
}
}
...
This is my custom class
public class SendMessage
{
public string chatID { get; set; }
public string messageText { get; set; }
}