Help understanding routes

Hi,

I am currently messing round with CI4 and I am having issue with understanding the routing.

I have a controller that I just randomly made:

PHP Code:

<?php

namespace App\Controllers;

use CodeIgniter\Controller;

class Login extends BaseController {
    
     public function index() {
         
        
        return view('welcome_message');
    }
    
} 


now if I direct to login it works just fine without a line in routes.  if I add a route like so:

PHP Code:

$routes->get('admin', 'Login::index'); 


If I now go to /admin then it work and shows me login.  The issue is then if I move Login.php controller into a folder called admin in the controllers folder and change the route to:

PHP Code:

$routes->get('admin', 'admin/Login::index');

or 

$routes->get('admin', 'admin\Login::index'); 


I get:

Controller or its method is not found: \App\Controllers\admin\Login::index

and I cannot for the life of me figure out why this doesn't work.  Can anyone enlighten me on why this isn't working please?

Thanks,

Doomie