Stripe webhooks are the nervous system of your billing. When they fail, things break silently.

Stripe webhook reliability failures have consistent root causes:

Missing signature verification. Stripe signs every webhook with a secret. Verifying the signature confirms the event came from Stripe. Without verification: anyone can POST fake events to your endpoint. Fix: stripe.webhooks.constructEvent(body, sig, secret) before processing.

Not returning 200 quickly enough. Stripe expects a 200 response within 30 seconds. If your handler does slow database work before responding, Stripe may time out and retry. Fix: return 200 immediately, process the event asynchronously via a background job.

Duplicate processing. Stripe retries events that receive a non-200 response. If your handler succeeds but returns 500 (an error in a different code path), Stripe retries. The event gets processed twice. Fix: idempotent handlers — check if the event ID has already been processed before doing work.

// Store processed event IDs
async function handleStripeWebhook(event: Stripe.Event) {
  const existing = await db.query.stripeEvents.findFirst({
    where: eq(stripeEvents.eventId, event.id)
  });
  if (existing) return; // Already processed
  
  // Process the event
  await processEvent(event);
  
  // Mark as processed
  await db.insert(stripeEvents).values({ eventId: event.id });
}

Not handling all relevant events. Applications often only handle payment_intent.succeeded but miss invoice.payment_failed, customer.subscription.deleted, customer.subscription.updated. Fix: audit which events need to be handled for the billing model.

Webhook endpoint down during deploy. A restart during deployment causes events to fail. Stripe retries for 72 hours. Fix: ensure zero-downtime deployments or handle the retry window.