Rest server response error 500

Hi,
I'm setting up a website to act as our API to our internal database.
I think I'm going in the right direction but keep hitting a brick wall.
Server code and my test routine below.
Error2 = ProtocolError
Any pointers to resolve would be greatly appreciated!
Paul

What I have tried:

NOTE:
Just Added:

<system.web>
  <webServices>
    <protocols>
      <add name="HttpGet"/>
      <add name="HttpPost"/>
    </protocols>
  </webServices>
</system.web>

to Webserver config.
Now:
https://WEBSITE/service.asmx/TestRest
Returns:

<?xml version="1.0" encoding="UTF-8"?>
<string xmlns="http://localhost:51561/APIServer/">{"qtest":{"response":"hello"}}</string>

Getting better but my test site still fails. Same error as below.

Server Code: Service.vb file:

<WebService(Namespace:="http://localhost:51561/APIServer/")> _
<WebServiceBinding(ConformsTo:=WsiProfiles.BasicProfile1_1)> _
<Global.Microsoft.VisualBasic.CompilerServices.DesignerGenerated()> _
Public Class Service
    Inherits System.Web.Services.WebService

    <WebMethod()> _
    Public Function TestRest() As String

        Dim sjon As String = "{"
        sjon = sjon & """qtest"":{""response"":""hello""}"
        sjon = sjon & "}"

        Return sjon
    End Function
End Class

Service.asmx file:
<%@ WebService Language="vb" CodeBehind="~/App_Code/Service.vb" Class="Service" %>


Calling the Webserver with this:

        Dim returnedData As String = ""
        Dim error2 As String = ""

        Try

            Dim DataToSend As String = ""
 

            Dim urlLive As String = "https://WEBSITENAME/Service.asmx/TestRest"  

            Dim postAddress = New Uri(urlLive)

            Dim request = DirectCast(WebRequest.Create(postAddress), HttpWebRequest)

            request.Method = "POST"
            request.ContentType = "application/json"  

            request.Headers.Add("AcceptTypes", "text/plain")
            request.Headers.Add("Accept-Language", "en-US")
            request.Headers.Add("UserAgent", "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.1; Trident/5.0)")

            request.ContentLength = Len(DataToSend).ToString
 

            request.ProtocolVersion = HttpVersion.Version11

            Dim postByteData As Byte() = System.Text.UTF8Encoding.UTF8.GetBytes(DataToSend)
            request.ContentLength = postByteData.Length

            Using postStream As Stream = request.GetRequestStream()
                postStream.Write(postByteData, 0, postByteData.Length)
            End Using

            Using resp = TryCast(request.GetResponse(), HttpWebResponse)
                Dim reader = New StreamReader(resp.GetResponseStream())
                returnedData = reader.ReadToEnd()
            End Using

        Catch exw As WebException

            Try
                Dim httpResponse As HttpWebResponse = CType(exw.Response, HttpWebResponse)
                returnedData = "Error - " & CInt(httpResponse.StatusCode).ToString() & " - " & httpResponse.StatusCode.ToString()

                error2 = exw.Status.ToString

            Catch ex As Exception
                returnedData = "Error - Site"
            End Try

        Catch ex As Exception

            returnedData = "Error - Exception Error"

        End Try

        error2 = error2 & ""
        returnedData = returnedData & ""

Tags: Visual Basic, ASP.NET, REST, ASMX, HTTPS