Keysend / Spontaneous Payments

Keysend lets the sender pay a destination by node pubkey without the receiver issuing a BOLT11 invoice first. The sender includes the preimage as a TLV record in the onion; receiver extracts and fulfills.

Mechanism

Sender:
  preimage_random = random(32 bytes)
  payment_hash = SHA256(preimage_random)
  Build onion with TLV record:
    type 5482373484 ("keysend"): preimage_random
  HTLC for amount → forwarded via onion routing → arrives at destination.