Managers are unable to access account settings and therefore are unable to update billing or plan information. They are also not able to add new employees because doing so can impact your plan.
Please Note: Administrators are free accounts and you are able to add an unlimited amount of Administrators. If necessary, you can create an Administrator account for a Manager if you'd like them to have access to your account settings. You can use the same email address for the Manager, but they'll need a unique username.
Once you've created an additional account for them, you can upgrade them to an Administrator by going to Settings --> Administrators, finding their new account in the employee list and selecting "Add.