Crypto glossary
Lightning invoice (BOLT11)
A Lightning invoice is a payment request, usually a long string starting with lnbc or a QR code, that tells a wallet how much to pay, to whom and by when.
Defined in the BOLT11 specification, an invoice encodes the amount, the hash of a secret that the payer will learn when the payment completes, the recipient's node identity, a description, an expiry time and optional routing hints. Wallets scan it as a QR code or paste it, find a route through the network and pay it within seconds.
Invoices are the everyday interface of Lightning: point-of-sale apps generate one for each purchase, exchanges show one for deposits, and they can be created for a fixed amount or left open. The preimage revealed on payment serves as a cryptographic receipt. The newer BOLT12 standard introduces offers, reusable codes from which wallets fetch fresh invoices automatically and with better privacy.
Classic invoices are single-use: paying the same one twice is not possible, and reusing them for donations or recurring payments is awkward, which led to tools like Lightning addresses. They also expire, often after an hour, and reveal information such as the recipient's node. Paying an invoice to the wrong party is irreversible, so checking the amount and description matters.
Example
A café's tablet shows a QR code for an invoice of 4,500 sats that expires in ten minutes; a customer scans it with a Lightning wallet and the payment settles in about two seconds.