The reason that I'm not using Kagi (and some of my paid subscriptions) is that payments require login, and login makes it possible to track my search history. I

The reason that I'm not using Kagi (and some of my paid subscriptions) is that payments require login, and login makes it possible to track my search history. I'm happy with paying them with money, but not with my keywords. Is there some zero-knowledge protocol that could help here? In particular, to establish that a user is currently subscribed, without revealing which subscription they have?