How Do I get the private metafields or apps metafileds in checkout ui extension?

Hi, Im building an app with extensions using checkout ui api, however this has tobe with a montlhy plan for publish in shopify store, but i dont know how to access data from apps metafields, I was reading some post here saying the app change some private metafields when is subscribed, then i want to acces to that data in order to limit the use of the block extensions in checkout ui.

Im a bit lost in the documentation, all of the post reades goes in that way, any help will be appreciated.