Which webhook events fire for an underpayment or an overpayment?

invoice.underpaid fires when a real, confirmed on-chain payment arrives below the amount due, and invoice.overpaid fires when the invoice settles with a confirmed surplus. Both carry the invoice object with the amount expected versus the amount received, so you read the recorded shortfall or excess directly. Subscribe to both alongside invoice.paid — an endpoint that only listens for invoice.paid will miss every off-quote payment.