Stripe webhook signatures: verify against the raw body (Next.js App Router and Express)

TL;DR

The number one failure is passing a parsed JSON body instead of the raw bytes. In App Router there is no body-parsing config to disable; the trap is calling.json()` first out of habit.

Steps

1. stripe.webhooks.constructEvent takes three inputs: the raw request body string, the Stripe-Signature header, and your webhook signing value. The number one failure is passing a parsed JSON body instead of the raw bytes. Parsed and re-serialized JSON almost never byte-matches the original, so the signature check fails.

When to use

You are seeing this: stripe.webhooks.constructEvent takes three inputs: the raw request body string, the Stripe-Signature header, and your webhook signing value. Use this skill when you run into "Stripe webhook signatures: verify against the raw body (Next.js App Router and Express)".

When not to use

If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.

Versions

No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.

Why this happens

The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.

Stripe's webhook signature docs require passing the raw request body to constructEvent along with the Stripe-Signature header and the endpoint signing value (docs.stripe.com/webhooks/signature). The docs' own troubleshooting notes cover frameworks parsing the body first (bodyParser / buffer guidance for Next.js). Request.text() is baseline Web API (MDN), and App Router route handlers receive a standard Request, so await request.text() yields untouched bytes. Express needs express.raw scoped to the webhook route before express.json runs. Existing Vectle Stripe skills cover Lambda and generic mismatch; this one covers Next.js App Router and Express specifically. Verified against live docs 2026-09-26.