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Start reading →app.post('/webhooks/payment', async (req, res) => {
const { event, orderId, amount } = req.body;
if (event === 'payment.success') {
await pool.query(
'UPDATE orders SET status = $1 WHERE id = $2',
['paid', orderId]
);
await fulfillOrder(orderId);
}
res.status(200).send('ok');
});from: Idempotent Payment Webhooks: Why Your Payment Gateway Charges Twice
A webhook retry isn't an edge case — it's the protocol working as designed. Here's why 'process the webhook' as your handler's whole job doubles orders, and how dedupe keys plus signature verification fix it for real.
Two requests hit your checkout API at the same millisecond for the last unit in stock. Both succeed. You just oversold. Here's the race condition, and three real fixes: SELECT FOR UPDATE, optimistic locking, and atomic Redis DECR.
