If you are getting:
The Jetpack server was unable to communicate with your site [HTTP 406]
That usually means your hosting server has mod_security enabled and it is blocking the access. Contact your hosting support and ask them to disable mod_security to fix this issue.
Or, if you are getting:
The Jetpack server was unable to communicate with your site [HTTP 403]
That means the access to the xmlrpc.php is blocked. To solve it, you have to turn OFF this option: ”XMLRPC, Comments and Trackbacks blocked.” in your Sucuri Firewall Settings page. Just go to your Sucuri Firewall’s dashboard and click on Settings and then click on “Security”
Scroll down and you’ll see all your security options. Switch the option that says ”XMLRPC, Comments and Trackbacks blocked.” to OFF.
This is what you should see:
And that’s it!