Route Groups using array can't be done?

I'm trying to use route groups as below but it doesn't seem to work.
Any idea why? If it's a stupid mistake, help me out please, I'm blind after a long time checking this out. Thanks
$types = ['tesoro','cajas'];
foreach ($types as $type) {
    $group = "records/{$type}";
    $routes->group($group,['filter' => 'authGuard:allusers,agencyset'],function($routes){ ....

PS: If I use "records/cajas" directly, without the foreach it'll work fine.