Create Teams meeting error though HttpClient

Question

I'm creating an Application in C# to integrate with MS Teams. I was able to generate access token but getting error below when attempt to create a meeting using HttpClient() to Post to

"{"error":{"code":"BadRequest","message":"/me request is only valid with delegated authentication flow.",*

Am I missing something with the permission or the code is not correct? Thought?

generate access token code

var confidentialClientApp = ConfidentialClientApplicationBuilder
    .Create(clientId)
    .WithClientSecret(clientSecret)
    .WithAuthority(new Uri($"https://login.microsoftonline.com/{tenantId}"))
    .Build();

var scopes = new[] { $"https://graph.microsoft.com/.default" };
var authResult = await app.AcquireTokenForClient(scopes).ExecuteAsync();
accessToken = authResult.AccessToken;

here is create meeting code

        var meetingObject = new
        {
          subject = title,
          startDateTime = startTime,
          endDateTime = endTime,
          accessLevel = "everyone",
          entryExitAnnouncement= true,
          body = new { content = description },
          participants = new { 
                  organizier = new { 
                        identity = new { 
                                user = new { 
                                    id = "550fae72-d251-43ec-868c-373732c2704f" 
                                } 
                        } 
                  } 
          }
        };
        var jsonobj = Newtonsoft.Json.JsonConvert.SerializeObject(meetingObject);

        HttpResponseMessage servicerequest = null;
        TeamsMeetingEventObj meetingObj = new TeamsMeetingEventObj();
        try
        {
          using (HttpClient httpClient = new HttpClient())
          {
            httpClient.BaseAddress = new Uri("https://graph.microsoft.com/v1.0/me/onlineMeetings");
            httpClient.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));
            httpClient.DefaultRequestHeaders.Add("authorization", "Bearer " + accessToken + "");

            var content = new StringContent(jsonobj.ToString(), System.Text.Encoding.UTF8, "application/json");

            servicerequest = httpClient.PostAsync("https://graph.microsoft.com/v1.0/me/onlineMeetings", content).Result;
            string response = servicerequest.Content.ReadAsStringAsync().Result;
            meetingObj = JsonConvert.DeserializeObject<TeamsMeetingEventObj>(response);

            String OnlineTeamLink = meetingObj.join_WebUrl.ToString();

          }
        }
        catch (Exception ex)
        {
          meetingObj.general_message = "Exception: " + ex.Message;
        }