/// <summary>
/// Event handler for button Click event.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void btnStartNotifications_Click(object sender, EventArgs e)
{
	ReceiveNotifications();
}

/// <summary>
/// Use RingCentral C# Framework to access RingCentral API and request Subscription notifications.
/// </summary>
private async void ReceiveNotifications()
{
	try
	{
		// By default client talks to sandbox server (for production use "true" as third argument or actual server string e.g. "https://platform.devtest.ringcentral.com")
		RestClient rc = new RestClient(ringCentralAppKey, ringCentralAppSecret);

		// Authorization - If you use direct number as username, leave extension empty.
		await rc.Authorize(ringCentralUserName, "", ringCentralPassword);

		// Account and extension
		var account = rc.Restapi().Account();
		var extension = rc.Restapi().Account().Extension();

		// Create subscription to receive notifications
		var subscription = rc.Restapi().Subscription().New();
		rc.Restapi().Account().Extension().MessageStore(ringCentralAppKey);

		// Set filters for subscription
		subscription.EventFilters.Add("/restapi/v1.0/account/~/extension/~/message-store");
		subscription.EventFilters.Add("/restapi/v1.0/account/~/extension/~/presence?detailedTelephonyState=true");

		// Subscription Connect event handler
		subscription.ConnectEvent += ConnectHandler;

		// Subscription Notification event handler
		subscription.NotificationEvent += NotificationHandler;

		// Subscription Error event handler
		subscription.ErrorEvent += ErrorHandler;

		// Register subscription
		bool isRegistered = await subscription.Register();

		// Display registration status for subscription service
		txtNotifications.Text = "Subscription to Notification Success: " + isRegistered.ToString();
	}
	catch (Exception ex)
	{
		txtNotifications.Text = "ERROR: " + Environment.NewLine + ex.Message + ((ex.InnerException != null) ? ex.InnerException.Message : "");
		if (ex.Message != null)
		{
			Console.WriteLine("EXCEPTION / ERROR OCCURED: ");
			Console.WriteLine(ex.Message);
			if (ex.InnerException != null)
			{
				Console.WriteLine("MORE DETAILS: ");
				Console.WriteLine(ex.InnerException.Message);
			}
		}
	}
}

/// <summary>
/// Handler method for Notifications returned from Subscription service.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void NotificationHandler(object sender, NotificatioEventArgs e)
{
	txtNotifications.Text += "Notification: " + e.notification.ToString() + Environment.NewLine;
	Console.WriteLine("Notification: " + e.notification);
}

/// <summary>
/// Handler method for Errors returned from Subscription service.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void ErrorHandler(object sender, SubscriptionEventArgs e)
{
	txtNotifications.Text += "Error: " + e.Message + Environment.NewLine;
	Console.WriteLine("Error: " + e.Message);
}

/// <summary>
/// Handler method for Connection with Subscription service.
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void ConnectHandler(object sender, SubscriptionEventArgs e)
{
	txtNotifications.Text += "Connected: " + e.Message + Environment.NewLine;
	Console.WriteLine("Connected: " + e.Message);
}