What about making static invoices for cashu mints where people can redeem the same QR code for a set of payments connected to an inventory of products. So a cashu token pays out a small amount of satoshis for each product sold but uses the same pay string address? Is this possible? A non custodial static invoice for AMP on lightning still does not exist. This seems like it could be a feature for Phoenix server launching soon, But what about cashu?