code: public function send()
      {
          if (empty($this->message)) {
              throw new RuntimeException('No message to send.');
          }
  
          $transformer = new Transformer();
  
          if ($this->message instanceof RawMessage) {
              $message = $this->message->get('content');
          } else {
              $content = $transformer->transform($this->message);
              $message = [
                  'touser' => $this->to,
              ];
  
              if ($this->account) {
                  $message['customservice'] = ['kf_account' => $this->account];
              }
  
              $message = array_merge($message, $content);
          }
  
          return $this->staff->send($message);
      }
docs: Send the message.
  
  @return bool
  
  @throws RuntimeException