IN ASP.NET web application I want to convert a youtube links to MP3 file

Question

i want to just convert youtube links to MP3 file in asp.net.I have research about that and do the code but the code gives exception like below:

The underlying connection was closed: Could not establish trust relationship for the SSL/TLS secure channel. how to resolve that

    protected void Button1_Click(object sender, EventArgs e)
    {
        try
        {
            string url = TextBox1.Text;
            var source = @"C:\Users\Dipak";
            var youtube = YouTube.Default;
            var vid = youtube.GetVideo(url);
            File.WriteAllBytes(source + vid.FullName, vid.GetBytes());

            var inputFile = new MediaFile { Filename = source + vid.FullName };
            var outputFile = new MediaFile { Filename = $"{source + vid.FullName}.mp3" };

            using (var engine = new Engine())
            {
                engine.GetMetadata(inputFile);

                engine.Convert(inputFile, outputFile);
            }
        }
        catch (Exception exception)
        {

        }
    } 

I have found this types of code in Stack overflow but won't work