如何在WordPress中使用基于页面URL的二级菜单替换主菜单？

What I'm trying to do is to set a secondary menu on every page that matches the following URL (/example/*)

My problem is that there are some pages generated by the plugin & they aren't accessible in Pages - Wordpress dashboard. So I assigned a secondary menu for those who were there, but the moment I visit those who weren't it's loading primary menu.

I already tried some plugin-based solution and searched for the code-based solutions here, but the closest thing I could find was the code below that seems to be broken or incomplete.

  <?php 
    if (stripos($_SERVER['REQUEST_URI'], '/example/') !== true {
    //Set secondary menu here
    wp_nav_menu(array('menu' => 'Secondary menu'));
    } else {
    //Use primary menu`
    wp_nav_menu(array('menu' => 'Primary menu'));
    }