Definition
Underpayment
An underpayment is a payment arriving for less than the invoice, usually because the customer's wallet deducted the network fee from the amount sent rather than adding it. Providers credit, hold, or reject these differently, and almost none document which.
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Why does it happen?
Mostly wallet behaviour. A customer sends exactly the invoiced amount, and their wallet takes the network fee out of that total rather than adding it on top. What arrives is a few cents or a few dollars short.
It also happens when a customer types an amount manually, and the integration checklist covers testing for it, or when a quoted rate expires between the invoice being generated and the payment being broadcast.
How do providers handle it?
Three ways, and the differences are large.
Some credit the received amount and mark the order underpaid, leaving the decision with you. Some hold the payment pending a top-up, showing the customer a second request for the shortfall. Some reject it into a manual queue, which means somebody at your company resolves it by hand.
Which one your provider does is usually not written down anywhere. It is the single least documented behaviour in this category, and the catalogue records what each provider publishes, and it is why sending a deliberate 2% underpayment before launch is worth the few dollars it costs.
What should your shop do?
Decide a tolerance and apply it automatically. Many merchants accept shortfalls below a small threshold and fulfil the order, on the grounds that a fifty cent gap costs less than a support ticket. Above the threshold, request the difference or refund.
Whatever you choose, decide it before a customer creates the case rather than during. Accepting crypto payments covers the other failure paths.
Why the tolerance should be automatic
Because a human deciding each case costs more than the shortfall. A fifty cent gap resolved by a support agent is a loss; the same gap absorbed by a rule is a rounding error.
Set a threshold below which the order fulfils regardless, and put it in your terms so nobody has to make the call twice. Above the threshold, request the difference with a payment link rather than an explanation, since the customer already intended to pay and mostly just needs the easiest possible way to finish.
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Questions merchants ask
How common are underpayments?
Common enough to appear inside your first hundred orders. Wallets that deduct fees from the sent amount rather than adding to it produce them routinely, and the shortfall is usually small.
- Published with the index.