Issues prevent updates

[jcoles]

Attempts to do the first update after install (rc4) ends in failure. Is this a problem at my end? 
I have used various Debian-based Linux distros over the years, and usually apt or apt-get just works.
It looks like a problem at the repo end (I wouldn't be "signing" their repo, would I?) Is this just a matter of waiting?

sudo apt-get update
Hit:1 http://security.debian.org bookworm-security InRelease
Hit:2 http://deb.debian.org/debian bookworm-backports InRelease                                             
Hit:3 http://ftp.us.debian.org/debian bookworm-updates InRelease                                           
Get:4 http://la.mxrepo.com/antix/bookworm bookworm InRelease [27.4 kB]                 
Hit:5 http://ftp.de.debian.org/debian bookworm InRelease
Err:4 http://la.mxrepo.com/antix/bookworm bookworm InRelease
  The following signatures were invalid: EXPKEYSIG DB36CDF3452F0C20 antiX Linux repo <repo@antixlinux.com>
Reading package lists... Done
W: GPG error: http://la.mxrepo.com/antix/bookworm bookworm InRelease: The following signatures were invalid: EXPKEYSIG DB36CDF3452F0C20 antiX Linux repo <repo@antixlinux.com>
E: The repository 'http://la.mxrepo.com/antix/bookworm bookworm InRelease' 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.