code: public function validateChecksum($string)
      {
          $xml = new \SimpleXMLElement($string);
          $checksum = (string) $xml->Authentication->Checksum;
          $original = str_replace($checksum, $this->getMerchantPassword(), $string);
  
          return md5($original) == $checksum;
      }
docs: Validate Ecopayz XML message
  
  @param  string $string The xml string to validate
  @return bool   result