At the present time when approving leave from the Office 365 add-in, an error message is shown which disables this functionality.
This is a known issue that will be addressed in due course.
We apologise for any inconvenience caused.
Workaround: To approve leave on Appogee Leave, by clicking on the link to the request in the email.
This issue has now been resolved and the Office 365 add-in now correctly displays content relating to Leave request approvals.