define('PS_SHOP_PATH', '');
define('PS_WS_AUTH_KEY', '');
define('ORDER_ID', '');

require_once('./PSWebServiceLibrary.php');


try {

    $webService = new PrestaShopWebservice(PS_SHOP_PATH, PS_WS_AUTH_KEY, DEBUG);

    $xml = $webService->get([
        'resource' => 'order_carriers',
        'filter[id_order]' => ORDER_ID
    ]);

    $orderCarrierId = (int) $xml->order_carriers->order_carrier->attributes()->id;

    $xml = $webService->get([
        'resource' => 'order_carriers',
        'id' => $orderCarrierId,
    ]);

    $xml->order_carrier->tracking_number = "modificato";

    $opt = [
        'url' => PS_SHOP_PATH . 'api/order_carriers/' . $orderCarrierId . '?sendemail=1',
        'putXml' => $xml->asXML(),
        'id' => $orderCarrierId,
    ];

    $webService->edit($opt);
} catch (PrestaShopWebserviceException $ex) {
    echo 'Other error: <br />' . $ex->getMessage();
}