Calculation

Hello,
We want a field that auto minuses –
Cart Discount
Cart Subtotal
Order Total

We have set up a new field called – _pos_discount-test
and written this code –

add_filter('woe_get_order_product_value_pos_discount-test', function ($value, $order, $item, $product, $item_meta) {
// Calculate the subtotal
$subtotal = 0;
foreach ($order->get_items() as $order_item) {
$subtotal += $order_item->get_subtotal();
}
$cart_discount = $order->get_discount_total();
$order_total = $order->get_total();

$custom_field_value = $subtotal - $cart_discount - $order_total;

return $custom_field_value;

}, 10, 5);

Can you help on why this isn’t showing anything please?
many thanks