code: public function getData()
      {
          $this->validate(
              'merchantId',
              'merchantPassword'
          );
  
          if ($xml = $this->httpRequest->request->get('XML')) {
  
              if (!$this->validateChecksum($xml)) {
                  throw new InvalidRequestException('Invalid XML checksum');
              }
  
              return new \SimpleXMLElement($xml);
  
          } elseif ($xml = $this->httpRequest->getContent()) {
              return new \SimpleXMLElement($xml);
  
          } else {
  
              throw new InvalidRequestException('Missing XML');
  
          }
      }
docs: Get the data for this request.
  
  @throws InvalidRequestException
  @return string                  request data