But, what does that mean? Peter can't have given up on us after all this years!!!?????
It means he forgot to renew his website certificate.
The problem should clear up when he renews it, or you can do what Ana suggests since you're not sending money or passwords or any sensitive information to the website.
You can read about certificates herehttps://www.makeuseof.com/tag/website-security-certificate-care/
The important thing to do when you get that browser warning is to check for details. You’ll be able to find out why the certificate was rejected, and decide for yourself if you want to continue and use the site anyway. If the certificate is expired, the website owner may have just forgotten to renew it on time.