code: private function getVariationIdentifier(OrderItem $orderItem)
      {
          if ($this->configService->get('variation_number_field', 'number') === 'number') {
              return $this->getVariationIdentifierFromNumber($orderItem->getNumber());
          }
  
          return $this->getVariationIdentifierByIdentifier($orderItem->getNumber());
      }
docs: @param OrderItem $orderItem
  
  @return int