Webhook error fixes

24 errors, each with the cause and a working fix.

• Stripe webhooks in Express: “Webhook payload must be provided as a string or a Buffer” and the raw body
  Fix Stripe's “Webhook payload must be provided as a string or a Buffer” in Express: give constructEvent the raw body, and keep express.json() off the webhook route.
• GitHub webhook signature mismatch: fixing X-Hub-Signature-256 verification
  Why your GitHub webhook X-Hub-Signature-256 check fails: no secret set, SHA-1 header, parsed body, form content type, wrong secret, or a proxy changing the payload. Working Node and Python code.
• Gumroad Ping not arriving at your webhook: checklist and fixes
  Gumroad sale pings not reaching your server? Check the Ping URL, form-encoded bodies, HTTPS, and response codes, and see how to verify a ping is real.
• Lemon Squeezy webhook signature verification failed: fixing X-Signature checks
  Lemon Squeezy signs webhooks with an HMAC-SHA256 hex digest of the raw body in X-Signature. Fix parsed bodies, wrong signing secrets and bad comparisons, with Node, Next.js and PHP code.
• MCP server not connecting: 6 config mistakes
  MCP server not showing up in VS Code, Cursor, Claude Code or Claude Desktop? Check the config key, placeholder syntax, Node version, Windows npx, deprecated packages and missing uv.
• Stripe webhook 400 in Next.js: "No signatures found matching the expected signature for payload"
  Fix Stripe webhook signature failures in Next.js, including “Webhook payload must be provided as a string or a Buffer”: read the raw body with req.text() or disable bodyParser.
• Stripe: “No signatures found matching the expected signature for payload” — how to fix
  Why Stripe webhook verification throws “No signatures found matching the expected signature for payload” and the exact fixes for Express, Next.js and Flask.
• Paddle webhook signature verification failed: Paddle-Signature (ts and h1) explained
  How Paddle Billing signs webhooks: HMAC-SHA256 of ts:rawBody with your notification destination secret, sent as Paddle-Signature ts=...;h1=.... Fix raw-body, secret and timestamp issues.
• PayPal IPN not received or IPN listener not working: troubleshooting checklist
  Why your PayPal IPN listener gets nothing or INVALID: check IPN History, return an empty 200, post back with cmd=_notify-validate to the right sandbox or live URL, and avoid redirects.
• Shopify webhook HMAC verification failing: how to fix X-Shopify-Hmac-Sha256 mismatches
  Why your Shopify webhook HMAC check fails, covering the raw body, base64 vs hex, and the wrong secret, with working Express, Flask and FastAPI code.
• Shopify webhook not firing or failing (401, timeouts, removed subscriptions): checklist
  Why Shopify webhooks stop arriving: non-2xx or 3xx responses, the 5-second timeout, subscriptions removed after 8 failed retries, HMAC rejections returning 401, and wrong secrets.
• Slack request signature verification failed (X-Slack-Signature): causes and fixes
  Why X-Slack-Signature checks fail: parsed instead of raw body, wrong secret (not the Signing Secret), stale X-Slack-Request-Timestamp, or a missing v0= prefix. Node and Python fixes.
• Square webhook signature verification failed: fixing x-square-hmacsha256-signature
  Square signs webhooks with HMAC-SHA256 over your exact notification URL plus the raw body, base64-encoded. Fix URL mismatches, wrong signature keys and parsed bodies, with Node and Python code.
• Stripe checkout.session.completed not firing or not received: checklist
  Why your webhook never gets checkout.session.completed: event not selected, wrong mode or account scope, Connect, CLI vs Dashboard endpoints, async payment methods, or failed deliveries.
• Stripe: “No stripe-signature header value was provided” — how to fix
  Why Stripe says “No stripe-signature header value was provided”: header-name casing, API Gateway and Lambda, proxies, and test requests. Fixes for Express, Next.js, FastAPI and Django.
• stripe.SignatureVerificationError in Python (FastAPI, Django, Flask): how to fix
  Fix stripe.SignatureVerificationError in Python: what each message means, and working FastAPI, Django and Flask webhook handlers that verify the raw body.
• Stripe: “Unable to extract timestamp and signatures from header” — how to fix
  Stripe throws “Unable to extract timestamp and signatures from header” when the value you pass isn't the Stripe-Signature header. Causes and fixes for Node, Next.js and Python.
• Stripe webhook duplicate events: making your handler idempotent
  Stripe can deliver the same webhook event more than once, and out of order. De-duplicate on event.id, handle the rare double Event case, and don't rely on event order.
• Stripe webhook failing with 301, 302, 307 or 308 redirect: how to fix
  Stripe treats any 3xx response to a webhook as a failed delivery. Fix www/apex, http to https, trailing-slash and Next.js middleware redirects on your webhook URL.
• Stripe webhook "timed out": why deliveries fail and how to respond fast enough
  Stripe marks a webhook delivery failed when your endpoint is too slow. Return 2xx before doing slow work, queue the rest, and recover missed events with delivery_success=false.
• Svix webhook verification failed (Clerk, Resend): “No matching signature found” fixes
  Why svix-signature checks fail for Clerk, Resend and other Svix webhooks: parsed JSON body, wrong whsec_ secret, missing svix-id/svix-timestamp headers, or clock skew. Node and Python fixes.
• Stripe webhook “Timestamp outside the tolerance zone” — causes and fixes
  What Stripe's “Timestamp outside the tolerance zone” webhook error means, and how to fix clock drift, delayed retries and replayed test events.
• Twilio webhook signature validation failed (X-Twilio-Signature): causes and fixes
  Why X-Twilio-Signature validation fails: proxy or ngrok URL mismatch, http vs https, re-encoded URLs, query params passed twice, wrong Auth Token, or JSON bodies. Node and Python fixes.
• WooCommerce webhook signature mismatch (X-WC-Webhook-Signature): causes and fixes
  Why X-WC-Webhook-Signature doesn't match: hashing parsed JSON, hex instead of base64, wrong webhook secret, or the unsigned ping on creation. Node and Python fixes, plus auto-disabled webhooks.