I want to update posts in frontend in my WordPress site. BUt update_post_meta doesnt work, I tested datas with echo, but they are working very well.

if(isset($_POST['save_button'])) {

    if (empty($_POST['title'])) {

        echo 'Error';

    } else {

        $post_id = $_POST['post_id'];

        update_post_meta($post_id,'post_title', $_POST['title']);

        echo $post_id; // works good;
        echo $_POST['title']; //works good;

        echo 'Saved';

    }

}