That's a good point since most might not be familiar with Cashu; defaulting to the Lightning address then Cashu if no Lightning address exists is probably a better way of handling it.

Ideally, there will be also be a NIP-89 handler that recommends the merchants' preferred app, and the client would link out to that app to finalize payment and/or marketplace implementers add support for the 'payment_preference' field in kind 0 (this is specced out in the [revised marketplace NIP](https://github.com/GammaMarkets/market-spec)).