Is there a sample powershell script that shows how to create implement the an API call?

I've tried following OAuth 2.0 - API - User Guide (manageengine.com) - with the self client, but it's throwing a 401 error (and that's before I hit the fact that I believe the token will expire and need a refresh token)

Just trying to work out if there's a known good implementation around such that I've got a working example to work with