Hikashop cart subtotal/total adaptation

-- url of the page with the problem -- : benwijn-d-o-t-nl.alvast-online.nl
-- HikaShop version -- : 4.0.1
-- Joomla version -- : 3.9.1
-- PHP version -- : 7.2.10
-- Browser(s) name and version -- : Chrome
-- Error-message(debug-mod must be tuned on) -- : None

Hi there,

I'm trying to make a hikashop plugin for 11the bottle for free in my shop.

I've succeeded in adapting the price with a plugin, but the subtotal and the total in the cart are not changing on 12th product.
I think i need function onBeforeCartSave(&$element,&$do) to do this. Do you have a documentation about the $element?
I don't know how to adress the product price in this element.

Or do i have to make a change in the subtotal/total calculation? I so, what file do i have to adapt?

Thx

My plugin for now:

<?php

defined('_JEXEC') or die;
?><?php

class plgHikashopTwelveforeleven extends JPlugin {
		
	function plgTwelveforeleven(&$subject, $config){
		parent::__construct($subject, $config);
	}
		
	//function onBeforeCartSave(&$element,&$do) {
		//$lst1 = $element->cart_products;
		//foreach ($lst1 as $item) {
			//if ($item->cart_product_total_quantity == 12) {
				//$element=null;
				//$item->prices[0]->price_value_with_tax = 1 * $item->prices[0]->price_product_id;
				//}
		//}
	//}
	
	function onAfterCartProductsLoad(&$cart) {
		$lst1 = $cart->products;
		//echo"<pre>";var_dump($lst1);
		foreach ($lst1 as $item) {
			if ($item->cart_product_total_quantity == 12) {
				$item->prices[0]->price_value_with_tax = 11 * $item->prices[0]->price_id;
				}
		}
	}
	
}

I just added this code to the plugin. Works great. Thanks!

$tot = 0;
foreach ($lst as $item) {
$tot += $item->prices[0]->price_value_with_tax;
}
$cart->full_total->prices[0]->price_value_with_tax = $tot;