Why is lumen/laravel throwing error "Too few arguments passed" when using find/findmany?

I have an array of ids I want to use to get matching records from a table. Code looks like this:

$res = Extensiontables_Registry::findmany($ids[0])->get();

The full context looks like this:

  public function getData(Request $request){
    $ad_groupsOfUser = $this->getRoles($request);
    $ids = $ad_groupsOfUser->pluck('id');

    $res = Extensiontables_Registry::findmany($ids[0])->get();

    return response()->json($res, 200);
  }

  public function getRoles(Request $request)
  {
    $ad_groups = Ad_user::find($request->decodedToken->user_id)->ad_groups()->get();

    //return response()->json($roles, 200);
    return $ad_groups;
  }

$ids definitely is an array and contains values, I've debugged it. But why isn't it working with find/findmany? This is the full error I get:

 (1/1) ArgumentCountError

Too few arguments to function Illuminate\Support\Collection::get(), 0 passed in E:\aether-backend\app\Http\Controllers\UserController.php on line 49 and at least 1 expected