Super node setup, ZENcashofficial.github repository public key is missing

Dear ZEN users,

I am trying to setup a Horizen Super node.
I am stuck at step 3.8.
When I run:
sudo add-apt-repository ppa:certbot/certbot -y

I get:

GPG error: https://zencashofficial.github.io/repo bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY FB7053CE4991B669

Suggesting the repository is not signed. I can probably find a way to ignore it but that would be rather unsafe. I mean that is the point of having the package signed right, other wise the code might have been messed with?
Any suggestions on how to continue?

Regards,

Norin

Apologies, switching to the alternative key server which was mentioned in the documentation worked.
So running gpg --export 219F55740BBF7A1CE368BA45FB7053CE4991B669 | sudo apt-key add -

solved the issue. After which I could run

sudo add-apt-repository ppa:certbot/certbot -y

normally. Reading documentation properly is an art on its own