Mint 19.3 sha256sum bad signature

Hi all. I'm trying to verify the iso image for mint 19.3 cinnamon 64. I've followed the instructions on this page https://linuxmint.com/verify.php. I get "bad signature" when I check the sha256sum. The 256sum does match that of the iso but I want gpg reassurance.

I get no response from Mint and their forum is not publishing my query. Mint iso images were hacked a few years ago and you would think they would be on top of security.

Thanks.