When trying to upload a large file (archive) through File Manager in cPanel I came across this strange error:
An error occurred. Your account may be over its quota or you attempted to upload a folder.
Why strange ? Because everything in this account is set to unlimited. Just to be sure I double checked. Even the FTP user quota.
The domain was set to use Cloudflare and it blocked the upload going through.
The solution: disable caching in the DNS tab on Cloudflare, so it is set to “DNS only”.