Add extra fee based on shipping method in WooCommerce

// =========================================================================
// ADD EXTRA FEE BASED ON SHIPPING METHOD
// =========================================================================
add_action( 'woocommerce_cart_calculate_fees','wc_add_surcharge' ); 
function wc_add_surcharge() { 
    
    global $woocommerce; 

    if ( is_admin() && ! defined( 'DOING_AJAX' ) ) 
        
    return;
    
    $chosen_methods = WC()->session->get( 'chosen_shipping_methods' );
          
    $chosen_shipping = $chosen_methods[0];
    
    $fee = 10;

    if ( $chosen_shipping == 'flat_rate:2' ) {
        $woocommerce->cart->add_fee( 'Extra fee: ', $fee, true, 'standard' );  
    }
}