roykin/erp/erp_update_stock.php

<?php
error_reporting(E_ALL);
ini_set('display_errors', 1);
set_time_limit(0);

// Vendors
require_once 'ripcord/ripcord.php';
require '../config/config.inc.php';
require 'ErpTools.php';
require 'config.php';

if (empty($_GET['token']) || $_GET['token'] !== ERP_SCRIPT_TOKEN) {
    die;
}

$models = ripcord::client("$url/xmlrpc/2/object");

$d = Db::getInstance();

$sql = 'SELECT `id_erp` FROM `'._DB_PREFIX_.'product_attribute` WHERE `id_erp` IS NOT NULL';
$ids_erp = $d->executeS($sql);

$ids = array();
foreach ($ids_erp as $key => $value) {
    if ($value['id_erp']) {
        $ids[] = (int)$value['id_erp'];
    }
}

$variants = $models->execute_kw($db, $uid, $password,
    'product.product', 'read', [$ids] , array('fields' => array('qty_available', 'id'))
);

foreach ($variants as $key => $variant) {
    $sql = 'UPDATE `'._DB_PREFIX_.'product_attribute` pa, `'._DB_PREFIX_.'stock_available` sa
    SET sa.`quantity` = '.(int)$variant['qty_available'].'
    WHERE pa.`id_erp` = '.(int)$variant['id'].'
    AND pa.`id_product_attribute` = sa.`id_product_attribute`';  
    $d->execute($sql);
}