Partial refunds supported and recorded

All-or-nothing refunds create a real business problem: a customer receives a damaged item among a multi-item order and is entitled to a partial refund. If the refund handler always calls stripe.refunds.create() with no amount parameter, the only option is a full refund — over-refunding destroys margin. The iso-25010:2011 functional correctness gap here is the absence of an amount field on the refund interface, and the GDPR Art. 17 dimension is the inability to correctly reflect the agreed financial correction in the stored record. The validation preventing total refunds from exceeding order total is equally important — without it, a bug or a race condition can issue more money than was collected.

Accept an amount parameter in your refund handler at app/api/orders/[id]/refund/route.ts, validate it against the refundable balance, and pass it explicitly to the payment provider.

const alreadyRefunded = order.refunds.reduce((sum, r) => sum + r.amount, 0)
const maxRefundable = order.total - alreadyRefunded

if (amount > maxRefundable) {
  return Response.json(
    { error: `Refund amount exceeds refundable balance of ${maxRefundable}` },
    { status: 400 }
  )
}

const providerRefund = await stripe.refunds.create({
  payment_intent: order.paymentIntentId,
  amount, // explicit partial amount in cents
})