Basically, the app registers a uri scheme (e.g. "lightning:") and that allows them to receive invoice payment intents from Amethyst. Then Minibits takes the Cashu token balance, converts it into Lightning, and pays it. So, as long as the Nostr client uses intents to call wallets, it should work.  

 Interesting, so it relies on lightning for interop? Sounds like a hack to me. Would it have been simpler if the spec were more abstract?