How do I configure server-side serial number validation?

CREATE DATABASE IF NOT EXISTS `mydb` DEFAULT CHARACTER SET utf8 COLLATE utf8_bin;
USE `mydb`;

-- --------------------------------------------------------
--
-- Table structure for table `clients`
--

CREATE TABLE IF NOT EXISTS `clients` (
  `client_id` int(10) unsigned NOT NULL auto_increment,
  `user_name` varchar(255) collate utf8_bin NOT NULL,
  `company` varchar(255) collate utf8_bin NOT NULL,
  `email` varchar(255) collate utf8_bin NOT NULL,
  `serial_no` varchar(255) collate utf8_bin NOT NULL,
  `additional_information` TEXT collate utf8_bin NOT NULL,
  PRIMARY KEY  (`client_id`),
  UNIQUE KEY `email` (`email`),
  UNIQUE KEY `serial` (`serial_no`)
) ENGINE=InnoDB  DEFAULT CHARSET=utf8 COLLATE=utf8_bin COMMENT='Our company clients' AUTO_INCREMENT=3 ;

--
-- Dumping data for table `clients`
--

INSERT INTO `clients` (`client_id`, `user_name`, `company`, `email`, `serial_no`, `additional_information`) VALUES
(1, 'John Doe', 'User Comp.', 'johnd@domain.com', '233-421-752-325', 'additional information'),
(2, 'User Name', 'Home', 'email@domain.com', '444-555-222-243', 'additional information');

<?php
// server response codes
define('LICENSE_VALID',   '601');
define('LICENSE_INVALID', '602');

$config = [
  // database connection parameters
  'database' => [
    'name' => 'mydb',
    'username' => 'root',
    'password' => '',
    'connection' => 'mysql:host=localhost',
    // set the PDO error mode to exception
    'options' => [
        PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION
    ]
  ],
  // client information table
  'clientsTableName' => 'clients',
  'serialNoTableCol' => 'serial_no'
];

/**
 * Server HTTP response to the query issued by Advanced Installer serial validation tool.
 *
 * @param boolean $isValid
 * @param string $postedSerial
 * @param int $languageId
 * @return string
 */
function serverResponse($isValid, $postedSerial = '', $languageId = 1033) {
  $newLine = "\n";

  // load error messages from your database, using "$languageId" for localization (optional)

  if ($postedSerial == '') {
    return LICENSE_INVALID . $newLine . 'Missing Serial Number!';
  }

  if ($isValid) {
    return LICENSE_VALID;
  } else {
    return LICENSE_INVALID . $newLine . 'Serial Number: ' . $postedSerial . ' is invalid!';
  }
}

/**
 * Connect to the database using PDO.
 * 
 * @param array $config
 * @return PDO
 */
function openDbConnection($config, $serialNumber, $languageId) {
  try {
    $connection = new PDO(
      $config['connection'] . ';dbname=' . $config['name'],
      $config['username'],
      $config['password'],
      $config['options']
    );

    return $connection;
  } catch (PDOException $exception) {
    echo serverResponse(false, $serialNumber, $languageId);
    die();
  }
}

/**
 * Get the serial number from database.
 * 
 * @param string $serialNumber
 * @param string $languageId
 * @return int
 */
function getSerialNumber($serialNumber, $languageId) {
  $dbConnection = openDbConnection($GLOBALS['config']['database'], $serialNumber, $languageId);

  // prepare SQL statement
  $serialNumberQuery =  "SELECT `{$GLOBALS['config']['serialNoTableCol']}` FROM `{$GLOBALS['config']['clientsTableName']}` ";
  $serialNumberQuery .= "WHERE `{$GLOBALS['config']['serialNoTableCol']}` = {$dbConnection->quote($serialNumber)}";

  // execute query
  $result = $dbConnection->query($serialNumberQuery)->fetchColumn();

  return $result;
}

/**
 * Validate the given serial number.
 * 
 * @param string $serialNumber
 * @param int $languageId 
 * @param string $additionalInformation
 * @return string
 */
function validateSerialNumber($serialNumber, $languageId, $additionalInformation) {
  $result = getSerialNumber($serialNumber, $languageId);

  // get result set size
  if ($result == 0) {
    // serial number NOT found in database => issue error response
    echo serverResponse(false, $serialNumber, $languageId);
    die();
  } else {
    // serial number was found in database => issue SUCCESS response
    echo serverResponse(true, $serialNumber, $languageId);
    die();
  }
}

// Variables POSTed by Advanced Installer serial validation tool to this web page: "sn", "languageid".
if (isset($_POST['sn']) && trim($_POST['sn']) != '') {
  // get the serial number entered by the installing user in the "UserRegistrationDlg" dialog
  $serialNumber = trim($_POST['sn']);

  // get the system language ID of the user's machine
  // (you can use this parameter to display a localized error message taken from your database)
  $languageId = (int) $_POST['languageid'];

  // get the additional information entered by the installing user in the "UserRegistrationDlg" dialog
  $additionalInformation = $_POST['ai'];

  validateSerialNumber($serialNumber, $languageId, $additionalInformation);
} else {
  // issue error response
  echo serverResponse(false);
  die();
}
?>
      

http://www.example.com/validate.php