This article explains how an admin can allow managers to authorise an approval directly from an email.
To learn how to specify who approves what, please see: https://help.peoplehr.com/en/articles/3170614-multi-authorisation-workflows
Click the 'Settings' tab
Ensure you're in the Holiday & Absences tab
Scroll down and check the box, which says 'Authorise Holidays from Email':
To learn how a manager can approve holidays via the desktop or through email, please see: http://help.peoplehr.com/holiday-entitlements-requests/approvedecline-holidays
Thanks,
Customer Services Team.