WC_Abstract_Legacy_Order::add_coupon PHP Method

    public function add_coupon($code = array(), $discount = 0, $discount_tax = 0)
    {
        wc_deprecated_function('WC_Order::add_coupon', '2.7', 'Create new WC_Order_Item_Coupon object and add to order with WC_Order::add_item()');
        $item = new WC_Order_Item_Coupon();
        $item->set_props(array('code' => $code, 'discount' => $discount, 'discount_tax' => $discount_tax, 'order_id' => $this->get_id()));
        $item->save();
        $this->add_item($item);
        wc_do_deprecated_action('woocommerce_order_add_coupon', array($this->get_id(), $item->get_id(), $code, $discount, $discount_tax), '2.7', 'Use woocommerce_new_order_item action instead.');
        return $item->get_id();
    }