There are two licensing models for running enterprise Metabase.
With the standard model, which is what we are licensed for now, you configure a license key via UI and Metabase makes an outbound web request (to AWS) periodically to validate the key.
There is also an airgapped model, with different pricing, where you're provided a jar to install that handles licensing and time-validation. In this model, each upgrade requires a new jar.
https://www.metabase.com/docs/latest/paid-features/activating-the-enterprise-edition
We are running the open source version essentially airgapped, which blocks us from switching to enterprise.
We have the option of routing the request through a proxy, but it requires significant configuration and testing. We can do that work in a sandbox if have a test key (preferable) or are sure we don't invalidate the production key by using it on more than one instance.