Betfair NG API Navigation Application Menu error

Question

I am trying to create a Betfair app written in VB.NET using Betfair NG API. I am trying to request the navigation menu in VB.NET utilizing the following instructions, here, but I get error 400 Bad request. Could someone send me a code for doing so?

Sub GetNavigatorManu(ByVal SessToken As String, ByVal AppKey As String)

    Dim request As HttpWebRequest = Nothing
    Dim response As HttpWebResponse = Nothing


    Dim strResponseStatus As String = ""
    Try
        request = WebRequest.Create(New Uri("https://api.betfair.com/exchange/betting/rest/v1/en/navigation/menu.json"))

        request.Accept = "application/json"
        request.Method = "GET"
        request.KeepAlive = True
        request.ContentType = "application/json"
        request.AutomaticDecompression = DecompressionMethods.GZip Or DecompressionMethods.Deflate
        request.Headers.Add("Accept-Encoding", "gzip,deflate")
        request.Headers.Add("X-Authentication", SessToken)
        request.Headers.Add("X-Application", AppKey)

        response = request.GetResponse()
        Display the status below 
        strResponseStatus = "Status is " & CType(response, HttpWebResponse).StatusCode

    Catch ex As Exception
        MsgBox("CreateRequest Error" & vbCrLf & ex.Message)
    End Try
    MsgBox(strResponseStatus)

End Sub