For a CSGO server the requirement is to use a verified steam account to download the content rather than anonymous, the control panel doesn't allow this.
I tried it manually but got this:
Can someone walk me through the steps of enabling httpcache to be written to and fixing this for a CSGO server?
I am aware some games are now requiring login with a Steam account to download the server, and SRCDS with pufferd will be able to handle this. That being said, I'm not sure what you're asking about with httpcache.
It looks like you're having permissions issues from your log. If you uploaded files using SFTP and the root account, you'll need to chown the files to the pp-user for the server. If you use the SFTP user provided in the panel that shouldn't be an issue.