This menu shows information on the subscription or no-subscription level of the node. This menu is also used to apply new subscriptions or check an existing subscription key expiry. The following screenshot shows subscription information of a production Proxmox node:

To apply or reapply a subscription key, click on the Upload Subscription Key button and enter the key you got directly from Proxmox or an authorized reseller, and then click on OK, as shown in the following screenshot: