Lightning and other payment methods

Mint and melt need a payment method. Most Cashu mints use Lightning.

NUT-23 is BOLT11 invoices. NUT-25 is BOLT12 offers. NUT-24 is HTTP 402, so a website can demand Cashu for a resource. NUT-30 mints and melts over on-chain bitcoin.

These specs plug into NUT-04 and NUT-05. Read those first if this chapter feels like it is missing the beginning of the story.