Lets encrypt SSL cannot be added (The Let's Encrypt HTTP challenge failed)
If you receive an error message such as "The Let's Encrypt HTTP challenge failed" while trying to issue SSL on your domain, please try renaming or deleting .htaccess file.
.htaccess file can be found in the public_html folder. In order to see it, you will need to make sure that your File Manager (or FTP client) is setup to 'show hidden files'. This option can be checked in 'settings' panel which is located on the top-right corner in your File Manager.
Once this is done, you should be able to issue SSL on your domain.