C# class file to send SMS by adding Google Calender Event who in turn sends SMS notifications & reminder provided the user enabled SMS alert in his/her google calendar settings.

GoogleCalendarEventSmsNotifier

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Security.Cryptography.X509Certificates;
using Google.Apis.Auth.OAuth2;
using Google.Apis.Calendar.v3;
using Google.Apis.Services;
using Google.Apis.Calendar.v3.Data;
using System.Dynamic;

    /// <summary>
    /// C# class file to send SMS by adding Google Calender Event who in turn sends SMS notifications & reminder provided the user enabled SMS alert in his/her google calendar settings.
    /// </summary>
    public class GoogleCalendarEventSmsNotifier
    {
        String _keyfile;
        String _keyPassword;
        String _serviceAccountEmail;
        String _calendarId;
        public GoogleCalendarEventSmsNotifier(String keyFile, String keyPassword, String serviceAccountEmail, String calendarId)
        {
            _keyfile = keyFile;
            _keyPassword = keyPassword;
            _serviceAccountEmail = serviceAccountEmail;
            _calendarId = calendarId;
        }

        /// <summary>
        /// Creates Google Calendar Event with reminder and notification enabled.
        /// </summary>
        /// <example>
        /// dynamic request = new ExpandoObject();
        /// request.timeZone = "Asia/Calcutta";
        /// request.eventStart = Convert.ToDateTime(DateTime.UtcNow.AddSeconds(80).ToString("yyyy-MM-dd'T'HH:mm:ssZ"));
        /// request.eventEnd = Convert.ToDateTime(DateTime.UtcNow.AddSeconds(80).AddMinutes(15).ToString("yyyy-MM-dd'T'HH:mm:ssZ"));
        /// request.eventReminderMinutes = 1;
        /// request.eventSummary = "Approval Request";
        /// request.eventDescription = "Samy has sent a approval for expense claim";
        /// request.eventOrganizerName = "VM Workflow";
        /// request.eventOrganizerEmail = "mobility@organizeremail.com";
        /// request.eventCreatorName = "VM Workflow";
        /// request.eventCreatorEmail = "mobility@creatoremail.com";
        /// request.eventAttendeeName = "Johny Michael";
        /// request.eventAttendeeEmail = "attendee@youremail.com";
        /// request.eventLocation = "My Apps";
        /// 
        /// GoogleCalendarEventSmsNotifier smsNotifier = new GoogleCalendarEventSmsNotifier(Server.MapPath(@"/key.p12"), "your-password", "youraccount@developer.gserviceaccount.com","primary");
        /// dynamic response = smsNotifier.SendSms(request);
        /// 
        /// </example>
        /// <param name="request">Dynamic request object</param>
        /// <returns>Dynamic response object</returns>
        public dynamic SendSms(dynamic request)
        {
            dynamic response = new ExpandoObject();
            response.Status = true;
            var certificate = new X509Certificate2(_keyfile, _keyPassword, X509KeyStorageFlags.Exportable);

            ServiceAccountCredential credential = new ServiceAccountCredential(
               new ServiceAccountCredential.Initializer(_serviceAccountEmail)
               {
                   Scopes = new[] { CalendarService.Scope.Calendar }
               }.FromCertificate(certificate));

            // Create the service.
            var service = new CalendarService(new BaseClientService.Initializer()
            {
                HttpClientInitializer = credential,
                ApplicationName = "Calendar Api",
                ApiKey = ""
            });

                 
            Google.Apis.Calendar.v3.Data.Event newEvent = new Google.Apis.Calendar.v3.Data.Event();           
            newEvent.Kind = "calendar#event";

           
            EventDateTime EStart = new EventDateTime();
            EStart.DateTime = request.eventStart;
            newEvent.Start = EStart;
            EventDateTime EEnd = new EventDateTime();
            EEnd.DateTime = request.eventEnd;
            newEvent.End = EEnd;


            newEvent.Reminders = new Event.RemindersData();
            newEvent.Reminders.UseDefault = false;
            EventReminder ER = new EventReminder();
            ER.Method = "sms";
            ER.Minutes = request.eventReminderMinutes;
            newEvent.Reminders.Overrides = new List<EventReminder>();
            newEvent.Reminders.Overrides.Add(ER);


            newEvent.Summary = request.eventSummary;
            newEvent.Description = request.eventDescription;
            newEvent.Organizer = new Event.OrganizerData() { DisplayName = request.eventOrganizerName, Email = request.eventOrganizerEmail, Self = true };
            newEvent.Creator = new Event.CreatorData() { DisplayName = request.eventCreatorName, Email = request.eventCreatorEmail, Self = true };


            EventAttendee attendee = new EventAttendee();
            attendee.Email = request.eventAttendeeEmail;
            attendee.DisplayName = request.eventAttendeeName;
            newEvent.Location = request.eventLocation;

            IList<EventAttendee> myAttendees = new List<EventAttendee>();
            myAttendees.Add(attendee);
            newEvent.Attendees = myAttendees;
            

            try
            {
                //service.Calendars.Insert(newCal).Execute();                
                EventsResource.InsertRequest insertRequest = service.Events.Insert(newEvent, _calendarId);
                insertRequest.SendNotifications = true;
               response.Result = insertRequest.Execute();
            }
            catch (Exception e)
            {
                response.Status = false;
                response.Exception = e;
                response.Message = e.Message;
            }
            response.Message = "SMS has been sent successfully";
            return response;

        }
    }