C# - trying to retrieve languages json, timeline and more for my api results in bad authentication 401/403

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c# - trying to retrieve languages json, timeline and more for my api results in bad authentication 401/403
i send consumer key and consumer key secret get bearer. i send bearer (even tried to encode it bas 64) but got unauthorized or bad request:( (401/403) - i’m using oauth2
attaching my code (would appriciate any help i can get)

try
            {
                var postBody = "grant_type=client_credentials";
                HttpWebRequest authRequest = (HttpWebRequest)WebRequest.Create(string.Format("https://api.twitter.com/oauth2/token"));

                authRequest.Headers.Add("Authorization", GetAuthHeader(fetchParams));
                authRequest.Method = "POST";
                authRequest.ContentType = "application/x-www-form-urlencoded;charset=UTF-8";
                authRequest.AutomaticDecompression = DecompressionMethods.GZip | DecompressionMethods.Deflate;
                using (Stream stream = authRequest.GetRequestStream())
                {
                    byte[] content = ASCIIEncoding.ASCII.GetBytes(postBody);
                    stream.Write(content, 0, content.Length);
                }
                authRequest.Headers.Add("Accept-Encoding", "gzip");
				
                WebResponse authResponse = authRequest.GetResponse();

                // deserialize into an object
                TwitAuthenticateResponse twitAuthResponse;
                using (authResponse)
                {
                    using (HttpWebResponse response = authRequest.GetResponse() as HttpWebResponse)
                    {
                        if (response.StatusCode != HttpStatusCode.OK)
                            throw new Exception(String.Format("Server error (HTTP {0}: {1}).",
                                response.StatusCode,
                                response.StatusDescription));

                        String responseString;
                        using (Stream stream = response.GetResponseStream())
                        {
                            StreamReader reader = new StreamReader(stream, Encoding.UTF8);
                            responseString = reader.ReadToEnd();
                            twitAuthResponse = JsonConvert.DeserializeObject<TwitAuthenticateResponse>(responseString);
                        }
                    }
                }

                // Do the timeline
                HttpWebRequest timeLineRequest = (HttpWebRequest)WebRequest.Create(string.Format("https://api.twitter.com/1.1/help/languages.json"));
                var timelineHeaderFormat = "{0} {1}";
                timeLineRequest.Headers.Add("Authorization",
                                            string.Format(timelineHeaderFormat, 
                                            twitAuthResponse.token_type, 
                                            Convert.ToBase64String(Encoding.UTF8.GetBytes(twitAuthResponse.access_token))));
                timeLineRequest.Headers.Add("Accept-Encoding", "gzip");
                timeLineRequest.Host = "api.twitter.com";
                timeLineRequest.ContentType = "application/json; charset=utf-8";
                timeLineRequest.Method = "GET";
                WebResponse timeLineResponse = timeLineRequest.GetResponse();
                var timeLineJson = string.Empty;
                using (timeLineResponse)
                {
                    using (var reader = new StreamReader(timeLineResponse.GetResponseStream()))
                    {
                        timeLineJson = reader.ReadToEnd();
                    }
                }
            }
            catch (WebException ex)
            {
                using (var stream = ex.Response.GetResponseStream())
                using (var reader = new StreamReader(stream))
                {
                    LocalLogger.WriteToEventLog(reader.ReadToEnd());
                }
            }
            catch (Exception e)
            {
                HandleServiceException(e);
            }