Looks like this is using the nostrconnect:// URI

https://github.com/nostr-protocol/nips/blob/master/46.md#direct-connection-initiated-by-the-client

The client creates a new key and puts it in the URI with some metadata, then the user can open the link in amber and it will ask the user to create a bunker.

Then when the user gets redirected back to the app the connection should be ready

The code I'm using in noStrudel is from my library applesauce https://hzrd149.github.io/applesauce/signers/nostr-connect.html#initiating-connection-from-client

Although it looks like this app is using https://www.npmjs.com/package/window.nostr.js which is just as good and maybe better suited for an app like cashu.me