/**
  * Ajax call for trigger send action manually
  * 
  * @since  1.1.0
  * 
  * @return [type] [description]
  */
 public function force_run()
 {
     check_ajax_referer('ajax_nonce', 'nonce');
     $subscriber = STC_Subscribe::get_instance();
     $subscriber->stc_send_email();
     _e('Scheduled event successfully executed', STC_TEXTDOMAIN);
     die;
 }
 /**
  * Single instance of this class.
  *
  * @since  1.0.0
  */
 public static function get_instance()
 {
     // If the single instance hasn't been set, set it now.
     if (null == self::$instance) {
         self::$instance = new self();
     }
     return self::$instance;
 }