Bolt cards give off unique URLs each time they are read via NFC. The URLs look like this:

lnurlw://card.yourdomain.com?p=A2EF40F6D46F1BB36E6EBF0114D4A464&c=F509EEA788E37E32

What if the customer gives the merchant a set of encrypted cashu notes the first time they pay them via LNURLw? The next time they pay, they can use the boltcard to reveal a decryption key to a cashu note so that the payment can be made even if the merchant is offline.