code: public function getCode()
      {
          $data = [
              'component_appid' => $this->getAppId(),
          ];
  
          $result = $this->parseJSON('json', [self::CREATE_PRE_AUTH_CODE, $data]);
  
          if (empty($result['pre_auth_code'])) {
              throw new InvalidArgumentException('Invalid response.');
          }
  
          return $result['pre_auth_code'];
      }
docs: Get pre auth code.
  
  @throws \EasyWeChat\Core\Exceptions\InvalidArgumentException
  
  @return string