In CharlieHR, holiday approval works by creating teams and then assigning Team Leads to those teams, or setting individual line managers.
That means those Team Leads/Line Managers and admin will be notified by email whenever someone in their team books holiday, and they can then make a decision.
Note: Super Admins will still be able to approve any holiday, they just won't be notified by email when it's booked.
Of course, you can create custom approvers if needed, by following the instructions in this article.