Is your site registered?
In regards to registration it is done by the administrator of your site by going to Administration > Site administration > Registration.
The choice to be private is up to you. Moodle doesn’t share your information with anyone. They don’t go into the site. They use the aggregated anonymous data to publish the statistics of the worldwide community and use other data to help them in their decision making around new features and plugins.
Enabling mobile app notifications
If you want to enable Mobile app notifications ie IM notifications to mobile devices, your site needs to be registered to be able to access the moodle messaging server https://messages.moodle.net/auth/login?next=%2F