Hello.
did you get this to work?
I am using R80.40, I am trying to allow the user the access to the web category "File Storage and Sharing" but block the category "file upload" to most of the users. With the testing rules have made it work for some applications, but not for all:
One drive, Google drive and terabox -> I was able to access the site and download and upload files to the application
Mega.com, megafire and wetransfer -> I was able to access the site and I was not able to upload any files. I got an error on the application about network issues, but not the custom blocked message we have configured on Checkpoint