As most customers don't use XML-RPC, it's disabled on our hosting by default to stop WordPress sites from being attacked, or used to attack other sites (https://blog.sucuri.net/2015/10/brute-force-amplification-attacks-against-wordpress-xmlrpc.html).

However, you can easily enable XML-RPC to support plugins such as JetPack and the WordPress mobile app by adding the following lines to the very top of your site's .htaccess file:

# Enable XML-RPC
<Files xmlrpc.php>
allow from all
</Files>

You can edit the .htaccess file either through FTP or the File Manager in cPanel. As the htaccess file is hidden, you'll need to ensure that your FTP client is configured to show hidden files, or the File Manager's "Show hidden files" option is ticked in the Settings.