LUD21: A proposal for currencies on payRequest

Protocol Design
1

Hi all,

I’m working on a proposal to add a currency list to the payRequest LNURL. This allows some cool features such as:

  • Allowing users to create invoices denominating amounts in other currencies based on the exchange rate of target wallets;
  • Allowing receivers to signal intent to convert the received BTC into another currency upon payment
  • Allowing senders services to inform of exchange rates if another currency besides btc is used on the sender side.

In the most general use case, we can have a remittance-like experience powered by Lightning and LNUrl.

Enabling wallets to create invoices based on the exchange rate of the target wallet is also very useful.

I would appreciate feedback on the PR.

We’re working on a implementation at Bipa (see bipa.app/.well-known/lnurlp/lorenzolfm). If any other service/wallet is interested in enabling support please reach out.

2

Notice that BOLT 12 already has support for non-native currencies and the exchange rate negotiation logic between sender and recipient to determine how many msat the foreign currency should map to.

Please ensure that the semantics of LNURL and BOLT12 match up, otherwise we end up with partially overlapping semantics and confusion for users.

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