This page can no longer be used for registration with sites other than Moodle.netand to check this error details this page also we get error This page does not exist yet.
Are you trying to register your site from Site administration / Registration (admin/registration/index.php)? Also, is your site customised at all?
Yes through Site administration / Registration also yes we have made multiple custom plugins, would that effect the registration?
Hmm, it sounds from the error message that there is a problem with some hub registration code.
In the past, Moodle sites could be registered with multiple community hubs, as described in the documentation Community hubs. However this functionality was removed from core in Moodle 3.4.
Are you using the local_hub plugin?
The main reason to we are trying to register our LMS on Moodle hub so we can use push notification in mobile app.
Are you able to upgrade your site, preferably to 3.7.4 or higher, otherwise to the latest 3.5 release (3.5.10) which includes the latest security fixes?