Please make sure to upload your website to the directory to which your domain is linked.
If you check the Domains page in the client area, you’ll see that your subdomain is linked to a directory named htdocs. But if you check the file manager, you’ll see that there is no such directory in your account, and all of your website files have been uploaded directly to your account’s home folder.
But since the server looks for a directory htdocs and it does not exist, your website only shows 404 Not Found errors.
To fix this, please create a new directory with the name htdocs, and move (or re-upload) your website files into it.