Error encountered when creating event in Microsoft Graph exp

Question

Error encountered when creating event in Microsoft Graph explorer for c#

 

Error message:

StatusCode: 403, ReasonPhrase: 'Forbidden',

 

Codes :

private static async Task<bool> CreateAppointmentAsync(HttpClient httpClient, EventModel eventModel)
{
var stringContent = JsonConvert.SerializeObject(eventModel);
string URL = GraphResource + GraphVersion + "/me/calendar/events";
var response = await httpClient.PostAsync(URL,
new StringContent(stringContent, Encoding.UTF8, "application/json"));
//var response = await httpClient.PostAsync(GraphResource + GraphVersion + "/me/events",
//new StringContent(stringContent, Encoding.UTF8, "application/json"));
return response.IsSuccessStatusCode;
}
Event model
public class EventModel
{
public string subject { get; set; }
public Start start { get; set; }
public End end { get; set; }
public List<Attendees> Attendees { get; set; }
}
public class Start
{
public DateTime dateTime { get; set; }
public string timeZone { get; set; }
}
public class End
{
public DateTime dateTime { get; set; }
public string timeZone { get; set; }
}
public class Attendees
{
public EmailAddress emailAddress { get; set; }
public string type { get; set; }
}