The WordPress app requires a service called XMLRPC to be functioning on your server. XMLRPC does not seem to be functioning on your site right now.
There are a few common causes to this. First, check that you are running the most recent version of WordPress on your site. This can also occur when a web hosting provider blocks XMLRPC. Please check with your hosting provider to find out if they allow XMLRPC on your site.
It can also happen if there is a plugin/theme that conflicts with it. To check whether a plugin is causing the conflict with the app, try deactivating all the plugins on your self-hosted site to see whether that fixes the issue.
You can find a list of known Plugin conflicts here.
