WooCommerce Checkout のラジオ ボタンの選択に基づいて動的な料金調整を実装するにはどうすればよいですか?

<code class="php">// Add a custom dynamic packaging fee
add_action( 'woocommerce_cart_calculate_fees', 'add_packaging_fee', 20, 1 );
function add_packaging_fee( $cart ) {
    if ( is_admin() &amp;&amp; ! defined( 'DOING_AJAX' ) )
        return;

    $packing_fee = WC()->session->get( 'chosen_packing' ); // Dynamic packing fee
    $fee = $packing_fee === 'box' ? 9.00 : 3.00;
    $cart->add_fee( __( 'Packaging fee', 'woocommerce' ), $fee );
}

// Add a custom radio fields for packaging selection
add_action( 'woocommerce_review_order_after_shipping', 'checkout_shipping_form_packing_addition', 20 );
function checkout_shipping_form_packing_addition() {
    $domain = 'woocommerce';

    echo '<tr class="packing-select"><th>' . __('Packing options', $domain) . '</th><td>';

    $chosen   = WC()->session->get('chosen_packing');
    $chosen   = empty($chosen) ? WC()->checkout->get_value('radio_packing') : $chosen;
    $chosen   = empty($chosen) ? 'bag' : $chosen;

    // Add a custom checkbox field
    woocommerce_form_field( 'radio_packing', array(
        'type' => 'radio',
        'class' => array( 'form-row-wide packing' ),
        'options' => array(
            'bag' => __('In a bag '.wc_price(3.00), $domain),
            'box' => __('In a gift box '.wc_price(9.00), $domain),
        ),
        'default' => $chosen,
    ), $chosen );

    echo '</td></tr>';
}</code>

<code class="javascript">// jQuery - Ajax script
add_action( 'wp_footer', 'checkout_shipping_packing_script' );
function checkout_shipping_packing_script() {
    if ( ! is_checkout() )
        return; // Only checkout page
    ?>
    <script type="text/javascript">
    jQuery( function($){
        $('form.checkout').on('change', 'input[name=radio_packing]', function(e){
            e.preventDefault();
            var p = $(this).val();
            $.ajax({
                type: 'POST',
                url: wc_checkout_params.ajax_url,
                data: {
                    'action': 'woo_get_ajax_data',
                    'packing': p,
                },
                success: function (result) {
                    $('body').trigger('update_checkout');
                    console.log('response: '+result); // just for testing | TO BE REMOVED
                },
                error: function(error){
                    console.log(error); // just for testing | TO BE REMOVED
                }
            });
        });
    });
    </script>
    <?php

}

// Php Ajax (Receiving request and saving to WC session)
add_action( 'wp_ajax_woo_get_ajax_data', 'woo_get_ajax_data' );
add_action( 'wp_ajax_nopriv_woo_get_ajax_data', 'woo_get_ajax_data' );
function woo_get_ajax_data() {
    if ( isset($_POST['packing']) ){
        $packing = sanitize_key( $_POST['packing'] );
        WC()->session->set('chosen_packing', $packing );
        echo json_encode( $packing );
    }
    die(); // Alway at the end (to avoid server error 500)
}</code>