code: public function onContentChange(ResourceEventInterface $event)
      {
          $shipment = $this->getShipmentFromEvent($event);
  
          //$this->invoiceSynchronizer->synchronize($shipment);
  
          $this->scheduleSaleContentChangeEvent($this->getSaleFromShipment($shipment));
      }
docs: Content change event handler.
  
  @param ResourceEventInterface $event