Nexmo API. Connection Forcibly Closed

Question

Sub SendReplyNexmo(reply As String)

        Dim w As New Net.WebClient
        Dim values As New Specialized.NameValueCollection
        values.Add("to", sender)
        values.Add("text", reply)
        values.Add("from", sentto)
        values.Add("api_key", nexAPIKey)
        values.Add("api_secret", nexAPISecret)
        Try
            w.UploadValues(New Uri("https://rest.nexmo.com/sms/json"), "POST", values)
            w.Dispose()
        Catch ex As Exception
            Dim logFile As IO.StreamWriter
            If IsNothing(HttpContext.Current) Then
                logFile = New IO.StreamWriter("C:\logs\SMSerror.log", True)
            Else
                logFile = New IO.StreamWriter(HttpContext.Current.Server.MapPath("/logs/SMSerror.log"), True)
            End If
            logFile.WriteLine(ex.Message)
            logFile.Dispose()
        End Try
    End Sub

This is the code that I am using to connect to the Nexmo API. Then, out of nowhere, my apps using this broke, and I am now getting the error.

The underlying connection was closed: An unexpected error occurred on a send.

I've tried setting a custom User Agent string, no change. I've tried searching docs.

ASP.NET 4.6.1 IIS 7.5 on Windows Server 2008 R2. Desktop versions run on windows 7

Answer 1

This is due to Nexmo disabling legacy TLS protocols. It now supports v1.2. You can find out more about it here. You could make a http request to the following url from your application to verify the TLS version, it should return a 200Ok if it supports 1.2 and 400 if not. In case it doesn't, this should solve the problem :

ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls12