When adding a new employee or editing an existing one you may encounter and issue where the employee you wish to assign as their manager does not appear in the dropdown.
If this happen you will need to check in 2 areas to see if the employee who you wish to make the employee's manager is set up correctly.
First area to check would be in:
People > Users
In there find the manager and make sure their User group is set as a manager.
If that is correctly the next area you will need to check would be:
Administration > HR > Data Management > Job Roles
You will need to make sure that the employees Job role is listed as a manager level job role, if the employee's job role is not a manager you will either need to move the employee into a job role that is a manger level role or edit their existing one to be a manager level role.
You can select the actions button next to the applicable job role, Edit and apply the manager level selection using the tick box.
Submit to save the change.
Another issue that might arise from them not having the correct role and user group can be approving time off and workflows where the manager will not be able to access any workflows that send to an employee's manager or view and approve any of their time off.