Thanks for the explanation Fabian, now it`s clear for me. Have a good day!see https://pom.proxmox.com/offline-keys.html#register-refresh-keys and https://pom.proxmox.com/offline-media.html#activating-an-subscription-key
basically, you give POM the server IDs and subscription keys for the offline systems. it will then validate them (since it has network access), and store the validated copy on a medium. if you then give the offline system access to the medium, the helper binary can find the pre-validated subscription info there and add it to the system.