How to display a message in AutomationEdge Process Studio?

I am designing a workflow in Automation Edge Process Studio where a user issues a book and the quantity in database must be reduced. The workflow takes Book Name and Quantity as input, checks availability, and updates the table.

If the book is unavailable, display the message “Book unavailable.”
which plugin should i use to here

We can use plugin “ Display MSG” or Alert() function in Modified JavaScript.