Why does Slim Framework work on my computer but not on the Internet server?

Question

index php.

<?php require_once"header.php"; ?>

<?php
    use Psr\Http\Message\ResponseInterface as Response;
    use Psr\Http\Message\ServerRequestInterface as Request;
    use Slim\Factory\AppFactory;

    require_once("vendor/autoload.php");

    $app = AppFactory::create();
    $app->addErrorMiddleware(true, true, true);

    $app->get('/', function (Request $request, Response $response, $args) 
    {
        require_once("nav/home.php");
        return $response;
    });
    $app->get('/sobre', function (Request $request, Response $response, $args) 
    {
        require_once("nav/sobre.php");
        return $response;
    });  
    $app->run();
?>

<?php require_once"footer.php";?>

When I access the home page ('/') it works, but when I click "/on" the server does not find the page, the route is not working.