The remote server returned an error: (403) Forbidden

Question

i am trying to upload video in youytube from my c# project

here is my design page

 

 

here is my code behind 

protected void btnsubmit_Click(object sender, EventArgs e)

{

YouTubeModel youtubeModel;

YouTubeRequestSettings settings;

YouTubeRequest request;

string devkey = "AIzaSyBzFdJApkJnjh6LCGpY-IIAku3dsjE5T3A";

string filename = Path.GetFileName(fileupload.FileName);

fileupload.SaveAs(Server.MapPath("~/App_Data") + filename);

string path = Server.MapPath("~/App_Data") + filename;

string filepath = Path.GetFullPath(path);

settings = new YouTubeRequestSettings("youtube", "535208901500 - 4f57lvr1vnequ7f3dqalug3eejj351c0.apps.googleusercontent.com", devkey);

request = new YouTubeRequest(settings);

settings.Timeout = 1000000000;

Video video = new Video();

video.Title = "Sample Video Title";

video.Description = "Sample Video Description";

video.Tags.Add(new MediaCategory("Comedy", YouTubeNameTable.CategorySchema));

video.Keywords = "Comedy";

video.Private =false;

video.MediaSource = new MediaFileSource(filepath, "video/quicktime");

Video createdVideo = request.Upload(video);

}

 i have used namespaces like that

 

using Google.GData.Extensions;

using Google.GData.Client;

using Google.GData.YouTube;

using Google.GData.Extensions.MediaRss;

using Google.YouTube;

 

 i already installed google Api v3 and i already generated ClientId key and Developer key 

what is the problem??i have already searched in google but unable to get proper solution..what should i do for solving this problem??can anyone help me please???