由于WooCommerce 3，你的实际代码是过时的，不方便...有多种方法：
1).**最佳方法：**在产品级别设置最小数量（对于产品类别）：

// On single product pages
add_filter( 'woocommerce_quantity_input_args', 'min_qty_filter_callback', 20, 2 );
function min_qty_filter_callback( $args, $product ) {
    $categories = array('Noten'); // The targeted product category(ies)
    $min_qty    = 5; // The minimum product quantity

    $product_id = $product->is_type('variation') ? $product->get_parent_id() : $product->get_id();

    if( has_term( $categories, 'product_cat', $product_id ) ){
        $args['min_value'] = $min_qty;
    }
    return $args;
}

// On shop and archives pages
add_filter( 'woocommerce_loop_add_to_cart_args', 'min_qty_loop_add_to_cart_args', 10, 2 );
function min_qty_loop_add_to_cart_args( $args, $product ) {
    $categories = array('Noten'); // The targeted product category
    $min_qty    = 5; // The minimum product quantity

    $product_id = $product->get_id();

    if( has_term( $categories, 'product_cat', $product_id ) ){
        $args['quantity'] = $min_qty;
    }
    return $args;
}

代码进入你的活动子主题（或活动主题）的functions.php文件。测试和工作。
2).替代方式：检查购物车项目并显示错误消息 （类似于您的代码）：

add_action( 'woocommerce_check_cart_items', 'wc_min_item_required_qty' );
function wc_min_item_required_qty() {
    $categories    = array('Noten'); // The targeted product category
    $min_item_qty  = 5; // Minimum Qty required (for each item)
    $display_error = false; // Initializing

    // Loop through cart items
    foreach(WC()->cart->get_cart() as $cart_item ) {
        $item_quantity = $cart_item['quantity']; // Cart item quantity
        $product_id    = $cart_item['product_id']; // The product ID

        // For cart items remaining to "Noten" producct category
        if( has_term( $categories, 'product_cat', $product_id ) && $item_quantity < $min_item_qty ) {
            wc_clear_notices(); // Clear all other notices

            // Add an error notice (and avoid checkout).
            wc_add_notice( sprintf( 'Bitte beachte die Mindestbestellmenge. Du brauchst mindestens %s Notenexemplare pro Arrangement. Aktuell hast du %s Stück in deinem Warenkorb.', $min_item_qty , $item_quantity ), 'error' );
            break; // Stop the loop
        }
    }
}

代码进入你的活动子主题（或活动主题）的functions.php文件。测试和工作。
要使其也适用于父产品类别，您还需要添加此自定义函数：

// Custom conditional function that handle parent product categories too
function has_product_categories( $categories, $product_id = 0 ) {
    $parent_term_ids = $categories_ids = array(); // Initializing
    $taxonomy        = 'product_cat';
    $product_id      = $product_id == 0 ? get_the_id() : $product_id;

    if( is_string( $categories ) ) {
        $categories = (array) $categories; // Convert string to array
    }

    // Convert categories term names and slugs to categories term ids
    foreach ( $categories as $category ){
        $result = (array) term_exists( $category, $taxonomy );
        if ( ! empty( $result ) ) {
            $categories_ids[] = reset($result);
        }
    }

    // Loop through the current product category terms to get only parent main category term
    foreach( get_the_terms( $product_id, $taxonomy ) as $term ){
        if( $term->parent > 0 ){
            $parent_term_ids[] = $term->parent; // Set the parent product category
            $parent_term_ids[] = $term->term_id; // (and the child)
        } else {
            $parent_term_ids[] = $term->term_id; // It is the Main category term and we set it.
        }
    }
    return array_intersect( $categories_ids, array_unique($parent_term_ids) ) ? true : false;
}

代码进入你的活动子主题（或活动主题）的functions.php文件。测试和工作。
然后在现有代码中，您将替换：

has_term( $category, 'product_cat', $product_id )

由

has_product_categories( $category, $product_id )

这将允许您处理父产品类别太多。

要使其适用于某个产品类别的项目总数，请使用以下代码：

add_action( 'woocommerce_check_cart_items', 'wc_min_item_required_qty' );
function wc_min_item_required_qty() {
    $categories    = '30'; // The targeted product category slug or ID
    $max_item_qty  = 10; // Minimum Qty required (for each item)
    $display_error = false; // Initializing

    // Loop through cart items
    foreach(WC()->cart->get_cart() as $cart_item ) {

        $product_id    = $cart_item['product_id']; // The product ID

    if( has_term( $categories, 'product_cat', $product_id )) {
        $item_quantity += $cart_item['quantity']; // Cart item quantity
    }
        // For cart items remaining to "Pizza" product category
        if( has_term( $categories, 'product_cat', $product_id ) && $item_quantity > $max_item_qty ) {

            wc_clear_notices(); // Clear all other notices

            // Add an error notice (and avoid checkout).
            wc_add_notice( sprintf( 'We can only take orders of up to 10 burgers per customer', $max_item_qty , $item_quantity ), 'error' );
            break; // Stop the loop
        }
    }
}

我正在使用此代码，但有2个问题.

• 即使有3个相同类别的项目，通知也会出现。因此，它是按每个项目的数量进行筛选的。我需要筛选器，当它是类别“25-suscripcion”的最小3个项目时，无论项目是什么。

• 这不是避免结帐，所以客户可以继续支付，即使通知出现。

add_action( 'woocommerce_check_cart_items', 'wc_min_item_required_qty' );
function wc_min_item_required_qty() {
$categories    = '25-suscripcion'; // The targeted product category slug or ID
$min_item_qty  = 3; // Minimum Qty required (for each item)
$display_error = false; // Initializing

// Loop through cart items
foreach(WC()->cart->get_cart() as $cart_item ) {

    $product_id    = $cart_item['product_id']; // The product ID

if( has_term( $categories, 'product_cat', $product_id )) {
    $item_quantity += $cart_item['quantity']; // Cart item quantity
}
    // For cart items remaining to "Pizza" product category
    if( has_term( $categories, 'product_cat', $product_id ) && $item_quantity < $min_item_qty ) {

        wc_clear_notices(); // Clear all other notices

        // Add an error notice (and avoid checkout).
        wc_add_notice( sprintf( 'We can only take orders of up to 10 burgers per customer', $min_item_qty , $item_quantity ), 'error' );
        break; // Stop the loop
    }
}

}
Ps：我对编程几乎一无所知，谢谢各位的帮助。