Нашла, у вас статья не дописана!
в файле system/library/cart/cart.php строку
$cart_query = $this->db->query("SELECT * FROM " . DB_PREFIX . "cart WHERE api_id = '" . (isset($this->session->data['api_id']) ? (int)$this->session->data['api_id'] : 0) . "' AND customer_id = '" . (int)$this->customer->getId() . "' AND session_id = '" . $this->db->escape($this->session->getId()) . "'");
Заменить на:
$cart_query = $this->db->query("SELECT * FROM " . DB_PREFIX . "cart WHERE api_id = '" . (isset($this->session->data['api_id']) ? (int)$this->session->data['api_id'] : 0) . "' AND customer_id = '" . (int)$this->customer->getId() . "' AND session_id = '" . $this->db->escape($this->session->getId()) . "' ORDER BY date_added ASC");