How to customize the seeded error Notification email generated when any leave transaction fails.

We want to customize the seeded error Notification email generated when any leave transaction fails for an employee. I have tried to customize the notification from below path: Click on Bell icon > Show All> Worklist > User name > Administration > Task Configuration > Search > AbsencesApproval. When we to "Notifications" section, "Error" task and then editing "Notification Header", custom text is not coming over email it still seeded email. Please help us how to configure the custom notification. We want the employees who has failed leave transaction should get notified over email so that they can resubmit or check with system admins.