Your theme is very old, which is why it won't validate anymore. It's connecting to our old validation domain/URL that doesn't exist anymore. The only workaround for this is manually installing the updated theme through FTP. Please check this https://theme.co/apex/forum/t/setup-updating-your-themes-and-plugins/62 under Manual Updates section.
Then after that, you should able to validate it
And before that, I recommend backing up your site. It seems everything is old and updating it directly will break it due to feature gaps. You can also test the update to the clone of your site as staging, and once fixed and working, you can then push back your staging copy to your main site. This might help https://www.youtube.com/watch?v=YtY-q5BBpeE