Question: 


User example can not select a carryover for next year. He does not have the option on his planned absences screen. How do I activate the option?


Answer: 


Reviewing the user, it would appear the ability to request transfer is disabled - please see below: 


As a result, the user will not be able to book the transfer. 

Please find the below guide:
Transfer Settings for Entitlement Carryover/Transfer