Redwood - HR Help Desk - Send Notification when Milestone is nearing - Object Workflow trigger issue

Summary:

I followed all the steps mentioned in the below doc, and i could not see any notification getting triggered.

Content (please ensure you mask any confidential information):

I created Email Templates outside Sandbox. Then, created Object Workflow inside Sandbox. Tagged the Email Template to the OW. Specified the Event Point and Condition for the milestone object workflow to trigger a workflow action when the Warned_Flag is set to Yes. And, Event Point = When a record is updated . In the Condition field, entered the following expression and published the Sandbox.

if (isAttributeChanged('WarnedFlag') && WarnedFlag=='Y')

return true;

Yet, the email is not getting triggered. Not sure how to crack this issue.