code: private function prepareCustomVariables()
      {
          if ($this->validationServiceId != null) {
              $serviceId = $this->validationServiceId;
          } else {
              $serviceId = $this->scopeConfig->getValue(Config::XML_FASTLY_SERVICE_ID);
          }
  
          $customVars =  [
              // Service ID
              'cd1'   =>  $serviceId,
              // isAPIKeyValid
              'cd2'   =>  ($this->isApiKeyValid()) ? 'yes' : 'no',
              // Website name
              'cd3'   =>  $this->getWebsiteName(),
              // Site domain
              'cd4'   =>  $this->request->getServer('HTTP_HOST'),
              // Site location
              'cd5'   =>  $this->getSiteLocation(),
              // Fastly module version
              'cd6'   =>  $this->helper->getModuleVersion(),
              // Fastly CID
              'cd7'   =>  $this->config->getCID(),
              // Anti spam protection
              'cd8'   =>  'fastlyext'
          ];
  
          return $customVars;
      }
docs: Prepares GA custom variables
  
  @return array
  @throws \Magento\Framework\Exception\NoSuchEntityException