Filters – What hook / action is executed when a field of the payment form is changed in WooCommerce

I've added a custom field to the WooCommerce checkout, as below.

oc_add_checkout_fields function ($ fields) {
$ fields['shipping_sub_area'] = table (
& # 39; Label & # 39; => __ (& # 39; Sub Area & # 39;),
& # 39; like & # 39; => & # 39 ;, select
& # 39; class & # 39; => array (& # 39; form-row-wide & # 39; update_totals_on_change & # 39;),
& # 39; priority & # 39; => 68,
& # 39; required & # 39; => true,
& # 39; id & # 39; => & # 39; th_sub_area & # 39;
& # 39; Options & # 39; => array (& # 39; => & # 39; Select & # 39;
& # 39; Clifton & # 39; => & # 39; Clifton1 & # 39;
& # 39; DHA & # 39; => & # 39; DHA1 & # 39;),
& # 39; custom_attributes & # 39; => array (),
& # 39; validate & # 39; => array (),
& # 39; default & # 39; => & # 39;
)

returns $ fields;
}
add_filter (& # 39; woocommerce_default_address_fields & # 39; oc_add_checkout_fields & # 39;);

When this field is changed, a preloader appears in the section of your order on the order form.
I want to do the following: If the value selected in the above field is Clifton1, add the 100 shipping fee to the cart, otherwise add the 300 shipping fee to the cart,

I've tried different hooks and actions but I can not get the value of a custom field added to the inside of the hook. For example, I used the following filter:

function filter_woocommerce_cart_shipping_packages ($ array) {
// let the magic of the filter come here
// die ("I am hre");
echo & # 39;
& # 39 ;;
print_r ($ array);
return $ array;
}; 

// add the filter
add_filter (& # 39; woocommerce_cart_shipping_packages & # 39 ;, & quot; filter_woocommerce_cart_shipping_packages & # 39 ;, 10, 1);

In $ array, I get:

[destination]    => Table
(
                [country] => PK
                [state] => TA
                [postcode] => 
                [city] => fds
                [address] => fsdf
                [address_1] => fsdf
                [address_2] => fsd
)

But I do not get the value of & # 39; shipping_sub_area & # 39; or th_sub_area.