$cpanel = new CPANEL(); // Connect to cPanel - only do this once.
  
// Create a subdomain.
$addsubdomain = $cpanel->api2(
    'SubDomain', 'addsubdomain',
        array(
        'domain'                => 'subdomain',
        'rootdomain'            => 'example.com',
        'dir'                   => '/public_html/directory_name',
        'disallowdot'           => '1',
    )
)