Cloudmin Xen GPL Debian repository - Binary is not signed

Hello,

When installing Cloudmin Xen GPL version i got this error on apt update:

Get:1 http://security.debian.org/debian-security stretch/updates InRelease [94.3 kB] Ign:2 http://ftp.us.debian.org/debian stretch InRelease
Ign:3 http://cloudmin.virtualmin.com/gpl/debian binary/ InRelease
Get:4 http://ftp.us.debian.org/debian stretch-updates InRelease [91.0 kB] Get:5 http://cloudmin.virtualmin.com/gpl/debian binary/ Release [1,382 B]
Get:6 http://cloudmin.virtualmin.com/gpl/debian binary/ Release.gpg [173 B]
Hit:7 http://ftp.us.debian.org/debian stretch Release
Ign:6 http://cloudmin.virtualmin.com/gpl/debian binary/ Release.gpg Reading package lists... Done
W: GPG error: http://cloudmin.virtualmin.com/gpl/debian binary/ Release: The following signatures were invalid: 1719003ACE3E5A41E2DE70DFD97A3AE911F63C51 E: The repository 'http://cloudmin.virtualmin.com/gpl/debian binary/ 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.

the installer script http://cloudmin.virtualmin.com/gpl/scripts/cloudmin-gpl-debian-install.sh did install the GPG key successfully.

i also tested APT repo of KVM: http://cloudmin.virtualmin.com/kvm/debian and the GPG key works, i could do apt update on KVM repository successfully.

so i'm suspecting there is something wrong with http://cloudmin.virtualmin.com/gpl/debian repository