The 400 Bad Request Problem
A webhook 400 bad request error hits your logs at 2 AM. Your integration was working yesterday. The provider (Stripe, GitHub, Shopify) is sending data, but your handler is rejecting it with HTTP 400. You've checked the endpoint URL. You've verified the domain. But the webhook malformed request keeps coming back.
This is one of the most frustrating webhook integration failures because the error message is intentionally vague—HTTP 400 means "I couldn't parse or validate what you sent," but not why. The root cause could be anywhere: raw body parsing, header mismatches, JSON encoding, signature verification, or middleware order. This guide walks you through the exact debugging steps and fixes that work.
Prerequisites
A running backend service (Node.js, Python, Go, etc.) with a webhook handler already defined
