基于 WooCommerce 中购物车项目数量的附加价格

Based on "woocommerce change price in checkout and cart page" answer code that change the total price in checkout page, I have added some extra code to count the products that user have in cart and if user had like 9 products in cart then add some price to total:

add_action( 'woocommerce_before_cart_totals', 'custom_cart_total' , 'get_cart_contents_count');
function custom_cart_total() {

    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
            return;
    if (WC()->cart->get_cart_contents_count() == 9){
        WC()->cart->total += 15;
    }
    elseif(WC()->cart->get_cart_contents_count() == 6){
       WC()->cart->total += 14; 
    }
    elseif(WC()->cart->get_cart_contents_count() == 4){
       WC()->cart->total += 13; 
    }

}

但它不起作用.这张图片将说明一切:

如果有人可以更正代码并告诉我如何显示图片中的消息，我将不胜感激

// Add a custom packing fee based on item count
add_action( 'woocommerce_cart_calculate_fees', 'custom_packing_fee', 10, 1 );
function custom_packing_fee( $cart ) {
    if ( is_admin() && ! defined( 'DOING_AJAX' ) )
        return;

    if ( did_action( 'woocommerce_cart_calculate_fees' ) >= 2 )
        return;

    $count = $cart->get_cart_contents_count();

    if ( $count >= 9 ){
        $fee = 15;
    }
    elseif( $count >= 6 && $count < 9 ){
        $fee = 14;
    }
    elseif( $count >= 4 && $count < 6 ){
        $fee = 13;
    }

    if ( isset($fee) && $fee > 0 ) {
        $label = sprintf( __('Box fee (%d items)'), $count);
        $cart->add_fee( $label, $fee, false );
    }
}