code: private function createRequest()
      {
          $xml = new DOMDocument();
          $xml->formatOutput = true;
  
          $avRequest = $xml->appendChild($xml->createElement('AddressValidationRequest'));
          $avRequest->setAttribute('xml:lang', 'en-US');
  
          $request = $avRequest->appendChild($xml->createElement('Request'));
  
          $node = $xml->importNode($this->createTransactionNode(), true);
          $request->appendChild($node);
  
          $request->appendChild($xml->createElement('RequestAction', 'AV'));
  
          if (null !== $this->address) {
              $addressNode = $avRequest->appendChild($xml->createElement('Address'));
  
              if ($this->address->getStateProvinceCode()) {
                  $addressNode->appendChild($xml->createElement('StateProvinceCode', $this->address->getStateProvinceCode()));
              }
              if ($this->address->getCity()) {
                  $addressNode->appendChild($xml->createElement('City', $this->address->getCity()));
              }
              if ($this->address->getCountryCode()) {
                  $addressNode->appendChild($xml->createElement('CountryCode', $this->address->getCountryCode()));
              }
              if ($this->address->getPostalCode()) {
                  $addressNode->appendChild($xml->createElement('PostalCode', $this->address->getPostalCode()));
              }
          }
  
          return $xml->saveXML();
      }
docs: Create the AV request.
  
  @return string