Uploading files to dropbox account programmatically

hi , my game is using dropbox api to sync files between many users , the problem is , all the api functions(downloading,creating folder,delete,move,getfiles) work perfectly except upload function , i took the source code and tested it in a whole new console application in visual studio and all function worked fine even upload, but unity dosn`t let me to do that instead it throws a web exception

"WebException: The remote server returned an error: (403) Forbidden. System.Net.HttpWebRequest.CheckFinalStatus (System.Net.WebAsyncResult result) System.Net.HttpWebRequest.SetResponseData (System.Net.WebConnectionData data)"

if think the problem is in (web requests logic) ,i think unity may be overriding (my request by another one , i don`t know ) the code for upload function is like this

     public Dropbox.Api.FileSystemInfo UploadFile2(string root, string path, string file)
     {
         var uri = new Uri(new Uri(DropboxRestApi.ApiContentServer),
             String.Format("files_put/{0}/{1}",
             root, UpperCaseUrlEncode(path)));
 
         var oauth = new OAuth();
         var requestUri = oauth.SignRequest(uri, _consumerKey, _consumerSecret,accessToken,"POST");
 
        
         var request = (HttpWebRequest)WebRequest.Create(requestUri);
         request.Method = WebRequestMethods.Http.Post;
         request.KeepAlive = true;
         request.Timeout = 1000 * 60*60;
         
         byte[] buffer;
         using (var fileStream = new FileStream(file, FileMode.Open, FileAccess.Read))
         {
             int length = (int)fileStream.Length;
             buffer = new byte[length];
             fileStream.Read(buffer, 0, length);
         }
 
         request.ContentLength = buffer.Length;
         using (var requestStream = request.GetRequestStream())
         {
             requestStream.Write(buffer, 0, buffer.Length);
         }
 
         var response = request.GetResponse();
         var reader = new StreamReader(response.GetResponseStream());
         var json = reader.ReadToEnd();
         return ParseJson<Dropbox.Api.FileSystemInfo>(json);
     }

NOTE: i added this line System.Net.ServicePointManager.ServerCertificateValidationCallback = Helper.Validator; Helper.Validator simply return true all time so i can validate all server certification