Order confirmation email sent on state transition to confirmed

A customer who pays for an order and receives no confirmation email has no evidence that the transaction occurred. From their perspective, they may have been charged without a successful order — leading to chargebacks, duplicated purchases, and unnecessary support contacts. This is an iso-25010:2011 reliability failure: the system accepted a payment but failed to complete its contractual obligation to the customer. The confirmation email is also the canonical moment to surface the order number, line items, and delivery estimate — omitting it makes every subsequent customer question ('where is my order?') harder to handle.

Add a confirmation email trigger in your payment webhook handler at app/api/webhooks/stripe/route.ts, fired immediately after the order transitions to 'confirmed'.

import { sendOrderConfirmationEmail } from '@/lib/email/order-emails'

case 'checkout.session.completed': {
  const order = await db.orders.findFirst({
    where: { stripeSessionId: event.data.object.id },
    include: { items: true, user: true },
  })
  await transitionOrder(order.id, 'confirmed', 'system', 'Payment received')
  await sendOrderConfirmationEmail({
    to: order.user.email,
    orderNumber: order.id,
    items: order.items,
    total: order.total,
  })
  break
}

If you use a job queue like BullMQ or Inngest, enqueue the email as a job rather than awaiting it inline to keep webhook response times under 5 seconds.