There is this PR to the spec -> https://github.com/nostr-protocol/nips/pull/1818

which is implemented in NDK, sample use -> https://github.com/relaystr/ndk/blob/master/packages/sample-app/lib/nwc_page.dart

It's already used in Yana and https://zap.stream/app

Don't know what shosho uses since it doesn't seem to be opensource...