A Lightning invoice is a payment request used on the Lightning Network to receive funds quickly and efficiently. It is a string of encoded data, often represented as a QR code or text, that contains all the necessary details for a transaction. These details typically include the payment amount, a description, the recipient’s node information, and an expiration time.

When someone wants to receive a payment, they generate a Lightning invoice using their Lightning wallet. The sender then scans the QR code or copies the invoice string into their wallet to complete the payment. Once processed, the transaction is settled almost instantly, with very low fees compared to traditional on-chain transactions on Bitcoin.

A key feature of Lightning invoices is that they are single-use and expire after a certain period, which improves security and prevents reuse. They are also secured using advanced cryptographic techniques such as hashed time-locked contracts (HTLCs), ensuring that payments are only completed if all conditions are met.

Lightning invoices make micropayments practical and seamless, allowing users to send even very small amounts efficiently. Overall, they play a crucial role in enabling fast, scalable, and user-friendly transactions within the Lightning Network ecosystem.