static void Main(string[] args)
    {
        ...

        var details = CallRestMethodAsync(url, filterObj);
        Console.Write(details);
        Console.ReadKey();

    }

    public static async Task<NotificationEvents> CallRestMethodAsync(string url, FilterPager filterPager = null)
    {
         ...
         var result = await response.Content.ReadAsStringAsync();
         return JsonConvert.DeserializeObject<NotificationEvents>(result, new JsonSerializerSettings { NullValueHandling = NullValueHandling.Ignore });
    }

System.Threading.Tasks.Task`1[NotificationsHandler.NotificationEvents]

static async Task Main(string[] args)
{
    ...

    var details = await CallRestMethodAsync(url, filterObj);
    Console.Write(details);
    Console.ReadKey();

}