Problem with base_url()

Hello guys,

I'm working on a new project, and I got a real problem ( I didn't do codeigniter/php since a long time)

I wan't to use base_url() in my view to redirect on another page, so i'm doing like this :
                            <li class="nav-main-item">
                                <a class="nav-main-link" href="<?= base_url('formulaire/inscription')?>">
                                    <span class="nav-main-link-name">Demande de compte</span>
                                </a>
                            </li>
But it's not working, it's only working if I put index.php in first.
In config.php I have:
$config['base_url'] = 'http://localhost/multi/';
$config['index_page'] = '';

I tried to change my htacces but it's not working...
Can you help me ?
Thanks