To update this thread, the issue was on the way the access token was being requested. When using Server to Server OAuth app, the grant type should always be account credentials, here is a helpful article for that:
https://devforum.zoom.us/t/how-to-user-server-to-sever-oauth-app-with-postman/70848/3
Also, the developer was using an endpoint that has been deprecated and a wrong query param, so make sure to use the right endpoints with the right params 