Not being able to create a directory is rarely a permission issue. The default permissions should be fine for letting WordPress create any file it needs. Typically, it’s only when people start tweaking with permissions it’s that things break.
But in your case, it’s not a permissions issue. Your account has reached the inode limit, as you can see in the control panel.
You can read more about that and get some basic information on how to solve this here:
I don’t think so. Whatever account the main domain is on has to be the account with the subdomain. If you have multiple domains (domain1.com, domain2.com, etc) you can have each on a different account.
Thanks
I have removed the subdomain and deleted website folders, but I couldn’t delete sub-domain named folder from the file manager. And the inodes is also not changed, it’s almost 6 hours.