code: private function getVariationIdentifierFromNumber($number)
      {
          $variations = $this->client->request('GET', 'items/variations', ['numberExact' => $number]);
  
          if (!empty($variations)) {
              $variation = array_shift($variations);
  
              return $variation['id'];
          }
  
          return 0;
      }
docs: @param string $number
  
  @return int