require 'vendor/autoload.php';
$server = new Flarum\Http\Server(
Flarum\Foundation\Site::fromPaths([
'base' => __DIR__,
'public' => __DIR__.,
'storage' => __DIR__.'/storage',
])
);
$server->listen();
After Flarum\Http\Server you were missing a (
Registration most likely fails because your mail settings are incorrect.