Add extra charges to specific shipping method in WooComerce

// =========================================================================
// ADD EXTRA FEE TO SPECIFIC SHIPPING METHOD
// =========================================================================
add_action('woocommerce_cart_calculate_fees', 'add_handling_fee_for_specific_shipping_method', 10, 1);
function add_handling_fee_for_specific_shipping_method($cart) {
    if (is_admin() && !defined('DOING_AJAX')) return;

    $chosen_methods = WC()->session->get('chosen_shipping_methods');
    $chosen_shipping = $chosen_methods[0];

    if ($chosen_shipping === 'flat_rate:5') {
        $fee = 500; // Kezelési költség mértéke
        $cart->add_fee(__('Kezelési költség postai kézbesítés esetén', 'woocommerce'), $fee);
    }
}