code: private function getVatRateIdentifier(array $variation)
      {
          $vatRateIdentity = $this->identityService->findOneBy([
              'adapterIdentifier' => $variation['vatId'],
              'adapterName' => PlentymarketsAdapter::NAME,
              'objectType' => VatRate::TYPE,
          ]);
  
          if (null === $vatRateIdentity) {
              throw new NotFoundException('missing mapping for vat rate');
          }
  
          return $vatRateIdentity->getObjectIdentifier();
      }
docs: @param array $variation
  
  @return string