If you want to move your subscription key to a new server, for example because you have replaced your hardware or you re-installed, you have to reissue your key via the client portal.
- Go to https://shop.maurer-it.com/clientarea.php?action=products
- Click on "View Details"
- On the "Management Actions" tab, choose "Reissue License"
If you have ordered your subscription via a Proxmox Partner, just contact them for help.