Symptoms
Cannot enable ModSecurity Atomicorp ruleset in Plesk on Debian-like installations with the following error in UI:
GPG error: https://updates.atomicorp.com/channels/tortix-common/debian buster InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY FFBD5D0A4520AFA9nE: The repository 'https://updates.atomicorp.com/channels/tortix-common/debian buster InRelease' is not signed.
Cause
Package manager is missing the required GPG key.
Resolution
1. Log in to Plesk via SSH
2. Install the key with the following CLI command:
apt-key adv --keyserver keyserver.ubuntu.com --recv-key FFBD5D0A4520AFA9