Stripe: “No signatures found matching the expected signature for payload” — how to fix

This error means the signature you computed from the request doesn't match the v1 value Stripe sent. In almost every case one of these is true:

1. The body was parsed before verification. Stripe signs the raw bytes. If express.json() (or a framework) parsed and re-serialized it, the bytes changed. Verify against the raw body.
2. Wrong secret. Use the endpoint's whsec_ signing secret, not your sk_ API key.
3. Test vs live mode. Each mode and each endpoint has its own secret; the Stripe CLI (stripe listen) prints yet another one.
4. A proxy changed the body (compression, re-encoding, trailing newline).

Express

app.post('/webhook', express.raw({ type: 'application/json' }), (req, res) => {
  const event = stripe.webhooks.constructEvent(req.body, req.headers['stripe-signature'], process.env.STRIPE_WEBHOOK_SECRET);
  res.sendStatus(200);
});

Register this route before any global app.use(express.json()).

Next.js (App Router)

export async function POST(req) {
  const body = await req.text();   // raw text, not req.json()
  const event = stripe.webhooks.constructEvent(body, req.headers.get('stripe-signature'), process.env.STRIPE_WEBHOOK_SECRET);
  return new Response('ok');
}

Flask

payload = request.get_data()       # raw bytes, not request.json
event = stripe.Webhook.construct_event(payload, request.headers['Stripe-Signature'], endpoint_secret)