more-then-7-warning.php

add_action( 'wp_loaded', function () {
	if ( is_admin() || WC()->cart->is_empty() ) {
        return;
    }
	
    $category_id = 106;
    $quantity_in_category = 0;

    foreach ( WC()->cart->get_cart_contents() as $cart_item ) {
        $product_id = $cart_item['product_id'];

        if ( has_term( $category_id, 'product_cat', $product_id ) ) {
            $quantity_in_category += $cart_item['quantity'];
        }
    }

    if ( $quantity_in_category > 7 ) {
        wc_add_notice( 'You cannot add more than 7 items from this category.', 'notice' ); // 'notice' will not block the add-to-cart
    }
}, 10, 0 );