code: public function execute(\Magento\Framework\Event\Observer $observer)
      {
          if ($this->config->getType() == Config::FASTLY && $this->config->isEnabled()) {
              $object = $observer->getEvent()->getObject();
  
              if ($object instanceof \Magento\Framework\DataObject\IdentityInterface && $this->canPurgeObject($object)) {
                  $tags = [];
                  foreach ($object->getIdentities() as $tag) {
                      $tag = $this->cacheTags->convertCacheTags($tag);
                      if (!in_array($tag, $this->alreadyPurged)) {
                          $tags[] = $tag;
                          $this->alreadyPurged[] = $tag;
                      }
                  }
  
                  if (!empty($tags)) {
                      $this->purgeCache->sendPurgeRequest(array_unique($tags));
                  }
              }
          }
      }
docs: If Fastly CDN is enabled it sends one purge request per tag
  
  @param \Magento\Framework\Event\Observer $observer
  @throws \Zend_Uri_Exception