Detect user removed from application

How to detect users removed from application in okta through rest api.

Is it some sort of event system or webhook system that you want to be able to use to have some logic on your application triggered when this happens out of band?

I just want to retrieve the details of users who remove from application through rest api.

If the user has been completely removed the resource will no longer exist. If the user has been deprovisioned, you can look for users with that status. Docs here: https://developer.okta.com/docs/api/resources/users.html#list-users-with-search