It's a Google issue not an issue with you. Someone forgot to update the
certificates for older gen 2 Chromecasts and Chromecast audio. You
should have gotten an email from Google like I got after I spent 3 hours
troubleshooting. My regular Chromecast...
My Chromecast 2 Gen have had the certificates updated and work fine. My
Chromecast audio which I removed from home is being recognized but I get
either "can not communicate with" or "can not authorize" Please advise
