These are two separate tools, they have separate logins, billing information, and functionality even though the admin area looks similar.
Hy.page = Is a Bio link builder that helps you sell products and memberships via your social media bio links. (similar to Linktree, Patreon etc)
Hyax = Is a much more advanced tool and something you would use to manage your entire business as it helps you create courses, sales funnels, stores, products as well as memberships. (similar to Kajabi, Podia, Clickfunnels etc.)