I want to add an aler(or notification) in function

I have a function that checks if products are in the same category and then if true it allows this product to be added to cart.

If a product does not pass validation I want notification or alert appear(This product in a different category). I do not know how to implement this. Could you please give me some advice.

add_filter('nav_menu_css_class', 'atg_menu_classes', 1, 3);

function is_product_the_same_cat($valid, $product_id, $quantity) {
    global $woocommerce; 
    if($woocommerce->cart->cart_contents_count == 0){ 
        return true; 
    } 
    foreach ( $woocommerce->cart->get_cart() as $cart_item_key => $values ) { 
        $_product = $values['data']; 
        $terms = get_the_terms( $_product->id, 'product_cat' ); 
        $target_terms = get_the_terms( $product_id, 'product_cat' ); 
        foreach ($terms as $term) { 
            $cat_ids[] = $term->term_id; 
        } 
        foreach ($target_terms as $term) { 
            $target_cat_ids[] = $term->term_id; 
        } 
    } 
    $same_cat = array_intersect($cat_ids, $target_cat_ids); 
    if(count($same_cat) > 0) return $valid; 
    else { 

        wp_safe_redirect(get_permalink( get_page_by_path( 'about' ) ) );
        exit();; 
    } 
} 
add_filter( 'woocommerce_add_to_cart_validation', 'is_product_the_same_cat',10,3);