<form action="" method="post">
    <input type="hidden" name="product_id" value="{$object.product_id}"/>
    <input type="hidden" name="action" value="add_product"/>
    <input type="hidden" name="quantity" value="1" />
    <span class="goods_item_title">{$object.pagetitle}</span>
    <span class="goods_item_price">{$object.sm_price|number_format:0:".":" "} <span>руб.</span></span>
    <button class="goods_item_button btn btn-success" type="submit">ЗАКАЗАТЬ!</button>
</form>     

test.ru/assets/components/basket/connectors/connector.php?action=products/add&product_id=20&quantity=1

test.ru/?action=add_product&product_id=16&quantity=1