Apt repo no longer signed

I started receiving this error today when running "apt-get update" on our chef server:

E: The repository 'https://packages.chef.io/repos/apt/stable focal Release' is not signed.
N: Updating from such a repository can't be done securely, and is therefore disabled by default.
N: See apt-secure(8) manpage for repository creation and user configuration details.

This is on an Ubuntu 20.04 server. The apt repo was added by following the steps here under Debian/Ubuntu: Chef Software Packages

Me and another person were chatting on Slack about this same issue. He was using the apt repo and I'm using the YUM repo.

This should be working again.