code: public function event(string $event): self
      {
          $events = [
              'MESSAGE_RECEIVED',
              'MESSAGE_SENT',
              'MESSAGE_FAILED',
          ];
          if (!in_array($event, $events)) {
              abort(500, sprintf('Event %s not available.', $event));
          }
  
          $this->event = $event;
  
          return $this;
      }
docs: Set default event.
  
  @param string $event
  
  @return self