你把代码放在哪里？可能没有执行此代码。

您应该将所有内容包装在一个函数中，并使用wp\\u head hook触发它。。。

<?php
add_action( \'wp_head\', \'woocommerce_conditional_hook\');
function woocommerce_conditional_hook(){
    function check_product_in_cart() {

        global $woocommerce;
        $box_found = false;
        $voucher_found = false;
        $other_products_found = false;

    //start of the loop that fetches the cart items
        foreach($woocommerce->cart->get_cart() as $cart_item_key => $values ) {
            $_product = $values[\'data\'];
            $terms = get_the_terms( $_product->id, \'product_cat\' );

        // second level loop search, in case some items have several categories
            foreach ($terms as $term) {
                $_categoryid = $term->term_id;

            //check if BOX product category is in card
                if ( $_categoryid === 103 ) {
                //category is in cart!
                    $box_found = true;
            } elseif ( $_categoryid === 106 ) { //check if VOUCHER product category is in card
                //category is in cart!
                $voucher_found = true;
            }else{
                $other_products_found = true;
            }
        }
    }
    return array($box_found, $voucher_found, $other_products_found);
}

    list($box_found, $voucher_found, $other_products_found) = check_product_in_cart();
    if(!$voucher_found){
        remove_action( \'woocommerce_checkout_after_customer_details\', array( $wc_checkout_add_ons->admin, \'render_add_ons\' ) );
        add_action( \'woocommerce_after_order_notes\', array( $wc_checkout_add_ons->admin, \'render_add_ons\' ) );
    }else{
        add_action( \'woocommerce_after_order_notes\', array( $wc_checkout_add_ons->admin, \'render_add_ons\' ) );
    }
}
?>