UserMessageUtil not working. Please help, anyone

I want to show a message whenever a user or group is added to a any project role. For which I am using in scriptrunner. But It does not show-up. what wrong am I doing. I am using listener feature and selected All Projects and firing it on the event ProjectRoleUpdatedEvent.

Though it does look that the script is run everytime I modify the roles in a project because it increments the count of executions with no failure. But no message is displayed. any help will be appreciated.

import com.onresolve.scriptrunner.runner.util.UserMessageUtil“role modified”)

I even tried in different browsers to be sure that it is not chrome issue. But still does not show the message anywhere.

When I use same code for Issue Created event, it works fine. The message is displayed.
But can anyone help me as why it does not work for ProjectRoleUpdatedEvent?
or should is it not the correct event that fires when a new user is added to any role in a Jira project.