Hi there @johnnydemarch ,
This error occurs when your webserver is serving HTTPS over a self-generated SSL certificate or if you are serving on a different domain than the SSL certificate was requested for.
How did you install vestaCP? Just by following the docs?
I checked your site and saw this is a sefl-signed certificate. If you don’t mind using this, you can just click advanced settings on your browser and continue using the site.
If you do mind, you should look into buying an SSL certificate (around 8$) or using Let’s Encrypt to get a free valid cert.
Hope this helps you. If not, let me know.