The raw-body rule

Providers sign the exact bytes they send. If your framework parses the JSON first, the bytes are gone and verification fails — this is the #1 webhook bug. Every adapter detects a pre-parsed body and returns 400 body_already_parsed instead of failing silently.

Framework	What to do
Express	Route-level express.raw({ type: 'application/json' }). If you need a global express.json(), add verify: (req, _res, buf) => { req.rawBody = buf } — the adapter reads req.rawBody first.
Fastify	Register the route inside a scoped plugin and call useRawJsonBody(scope).
NestJS	NestFactory.create(AppModule, { rawBody: true }). Don't set bodyParser: false.
Koa	Use @koa/bodyparser — it exposes ctx.request.rawBody.
Next.js App Router, Hono, Workers, Deno, Bun	Nothing. fetchWebhook reads request.arrayBuffer(). With Hono, pass c.req.raw.
Next.js Pages Router	export const config = { api: { bodyParser: false } } in the route file.
AWS Lambda	Nothing. Base64 bodies (isBase64Encoded) are decoded for you.
Django	Nothing — request.body is raw.
Flask	Nothing — the helper uses request.get_data(). Don't read request.json first.
FastAPI	Don't declare a Pydantic body parameter on the webhook route.

Proxies and gateways that re-encode JSON (some API gateways, some no-code tools) also break signatures — forward bodies untouched.