I was wrestling with updating some installed programs on my debian install. Finally, I decided to just run an apt update. Then it started failing when trying to accessing ‘packages.sury.org’ complaining about the key not matching. Eventually I found a post that said the key had changed and that the updated key needed to be downloaded “sudo wget -O /etc/apt/trusted.gpg.d/php.gpg https://packages.sury.org/php/apt.gpg”.
Hope this can help someone else.