No, subscription costs are based only on the employee total in your account, we do not charge extra for adding additional managers to your account. So you can add as many managers as needed, just be sure to set the permissions of each manager as appropriate.
Note that if managers need to be scheduled they will also have to be added as an employee, which would then count toward your employee total for pricing.
cost implication on the number of additional Manager accounts price for more managers pricing extra cost