Client Credentials vs Auth Code for server-side reporting app

Building a backend script to pull historical queue stats. Should I use client credentials grant or authorization code? The app doesn’t need user context, just bulk data access. I tried client credentials with this payload but getting 401:

{"grant_type": "client_credentials", "client_id": "my_id", "client_secret": "secret"}

Is the scope wrong? Docs say admin:report:read works but I’m getting insufficient_scope.