If your proxy blocks unknown URLs or URLs that are not on your whitelist please add the below appropriate URLs
...
Add all of the below for any of our Cloud Apps you use:
https://cdn.jsdelivr.net
https://cdnjs.cloudflare.com
https://connect-cdn.atl-paas.net
https://ac-cdn-mirror.herokuapp.com
AND one(or more) of the below URLs for the specific App you need:
Copy Page Tree
http://copy-page-hierarchy.herokuapp.com/
...