Please check the ‘Activity and Logging’ menu of the plugin, there you will see detailed info about this error.

Probably, this issue is caused by the not being made properly to my registration server.

If you get the error message from the plugin log, please send it to me, so I can check it. Also, it is very highly probably that you should contact your hosting provider’s support and ask them why connection to https://coderevolution.ro/ is returning the error shown in plugin log. Probably they have a firewall rule set up, that is blocking external connections. They should remove it and registration will work.