At this moment Fred and Commerce are not compatible.
As soon you have both installed you receive an HTTP Error 500 on Commerce url (Extras -> Commerce)
/manager/?a=index&namespace=commerce
How to re-create this problem:
Step 1: Install Commerce (Default setup with all checkboxed on)
Step 2: Install Fred
Step 3: Go to Extras -> Commerce
When you delete Fred, the page does work correctly again.
Error logs from server: https://pastebin.com/JAHWBD50
Currently running Modx Revolution 2.7.1 on Modx Cloud Servers with Php 7.1