AltoRouter never match subfolder

Question

I tried to use the AltoRouter on my webspace in a subfolder. But the matches always false!

I have this structure on my webspace

domain.com
--/2 --> subfolder
----index.php
----.htacces

My .htaccess file looks like this:

DirectoryIndex index.php

RewriteEngine on
RewriteBase /2/
RewriteCond %{REQUEST_FILENAME} !-f
RewriteRule ^ index.php [L]

So I setup up the router like this:

<?php

session_start();
require_once 'vendor/autoload.php';

use LemWebPortal\Config;

$latte = new Latte\Engine;

$router = new AltoRouter();
$router->setBasePath('/2/');

$router->map('GET', '/', function () {
    require __DIR__ . '/src/Init/index.php';
});

$router->map('GET', '/schulungsbedarf', function () {
    require __DIR__ . '/src/Init/courseRequest.php';
});

$match = $router->match();

if ($match && is_callable($match['target'])) {
    call_user_func_array($match['target'], $match['params']);
} else {
    // no route was matched
    header($_SERVER["SERVER_PROTOCOL"] . ' 404 Not Found');
}
echo '<pre>';
var_dump($match);

Now, when I call domain.com/2/or domain.com/2/schulungsbedarfI see an empty white page with this message:

bool(false)

What did I miss here?