Underpayments & Overpayments

Detection#

When a payment lands, the received amount is compared to the requested amount. Differences smaller than 0.1% are treated as rounding noise and complete normally - no customer sends exactly the displayed amount after fees. Beyond that deadband, the transaction is classified as underpaid and, depending on your setting, accepted or rejected.

Handling#

If "Consider transactions with underpayments as completed" is ON

Shortfalls under 5% are accepted: the transaction completes at the amount actually received, the fiat value is recalculated, and the customer sees a normal confirmation. This is the recommended setting for retail - it absorbs memo-fee rounding and volatile-coin slippage without support tickets.

Otherwise (or for shortfalls of 5% or more)

• The transaction is marked with an underpayment note: how much was received, how much is missing
• Status is set to rejected; no webhook fires and no fulfillment should occur
• The customer sees an "Underpayment" screen explaining the shortfall
• You are notified by email with an [Underpayment] subject, same as any sale notification

Resolve rejected underpayments manually: ask the customer to send the missing amount to the same address, or refund what arrived. Use Issue a refund on the transaction's detail panel (completed or rejected transactions) - it sends the received value back to the sender through your configured refund rail: your own Bitcoin/Ethereum node, or Coinbase with refunds enabled. Refunds only fire when the on-chain value and sender address match the transaction exactly; anything else is refused with a clear reason.

Overpayments#

There is no special overpayment path - a customer who sends more than requested simply completes the transaction at the requested amount, and the excess stays in their own wallet's receiving address (yours). If you want to return the difference, do it as a manual send or a payout.

Open amounts#

Checkouts with no fixed amount (pay-what-you-want) can never underpay by definition - any received amount completes, and no tax line is applied. See Invoicing.