Create table validation many to many in Laravel

I need to do a validation so that the database does not write repeated data to a table, which is an intermediate table of a many to many relationship, not having an id. Below is the code.

public function invite(Event $event)
{
    request()->validate([
        'guest_ids'=>'required' 
    ]);

    if(Auth::user()->id!=$event->user_id){
        return response(['error'=>'this event is not yours'],401);
    }

    $ids=explode(';',request()->guest_ids);
    foreach ($ids as $id) {
        if (request()->guest_id=request()->confirmed) {
            return "ok";
        } else {
            # code...
        }

        $event->guests()->attach(Guest::find($id));
    }
    $event->guests;
    return $event;
}

The table has the event_id, guest_id, and confirmed fields.