Employees cannot see the Personal Time Off feature under Time & Expenses on the main navigation.
This can happen if the security permissions of the employees restrict them from viewing the Personal Time Off Requests screen. To allow them access to PTO, you need to customize their security permissions and grant them access there. In particular, you need to make sure the Personal Time Off module is checked in the Security Profile of the employees. You can also customize individual security options under this module. Check CORE Help Center for details on customizing security permissions.
You also need to make sure the employees have access to the Time & Expense features of CORE via the right subscription. Please check with your Sales Account Manager to purchase the required subscriptions.