BillingWebhookKit

AI SaaS billing webhook checklist

AI-generated SaaS apps can reach checkout quickly, but billing code still needs boring proof before it takes money. Use this checklist before exposing a Lemon Squeezy, Stripe, Paddle, or Polar checkout link.

Open the free webhook generator Preview the CN¥69 Pro Kit

The launch rule

Do not treat a successful checkout page as a successful billing integration. A launch-ready AI SaaS billing route proves that the paid event is authentic, mapped to the right account, processed once, delivered privately, and reversible if a refund or rollback is needed.

Why AI-built billing routes fail

The handler parses JSON too early Signature checks fail when code verifies a reserialized body instead of the exact raw request body.
The paid state is trusted too loosely Order IDs, customer IDs, variant IDs, status fields, and currency need explicit contract assertions.
Retries run side effects twice Providers retry webhooks. Without idempotency, access grants, emails, invoices, or licenses duplicate.
Raw-body HMAC gate Verify Lemon Squeezy x-signature or Stripe-Signature before reading business fields.
Duplicate replay test Replay the same signed event three times and prove the entitlement mutation happens once.
Launch evidence packet Keep checkout, webhook, fulfillment, refund, and support evidence in a secret-free review note.

Minimum checklist before checkout goes public

1. Verify the exact raw body Read request text or bytes first, compute HMAC, compare the provider signature, then parse JSON.
2. Lock the event contract Assert event name, object type, object ID, variant or price ID, status, amount, currency, and customer mapping.
3. Build an idempotency key Use provider, event name, object ID, and payment or invoice scope before any side effect runs.
4. Replay duplicates in CI Send the same signed fixture repeatedly and expect one access grant, one email, and one fulfillment write.
5. Smoke test checkout to webhook Confirm the live checkout price, currency, success redirect, paid event delivery, and endpoint response.
6. Prove delivery and rollback Check private download delivery, checksum evidence, refund rollback, resend path, and support boundaries.

Where BillingWebhookKit fits

The free browser tools help generate fake payment webhook payloads, local signatures, cURL replay commands, idempotency keys, and review reports. The CN¥69 Pro Kit adds copy-ready fixtures, route handlers, Vitest signature tests, contract tests, duplicate replay tests, CI workflow notes, and launch review templates for teams that do not want to assemble the billing safety harness from scratch.

Lemon Squeezy payload generator Create fake payloads, signatures, and cURL replay commands without uploading secrets. Webhook idempotency key generator Build provider-scoped idempotency keys, SQL constraints, and duplicate replay test notes. Production checkout readiness report Generate a PR-ready report for live config, price, PayPal, signed webhooks, delivery, and rollback. Lemon Squeezy vs Stripe webhooks Compare provider-specific webhook launch checks before committing an AI SaaS checkout flow. Pricing ROI guide Compare free tools with the Pro Kit and decide whether CN¥69 saves enough manual setup time.

Can AI generate the webhook handler?

Yes, but review the raw-body path, signature comparison, trusted fields, idempotency guard, and retry behavior as if it were hand-written billing code. AI-generated code often looks complete before the failure cases are covered.

What blocks launch?

Block launch if the checkout price or currency is wrong, the webhook secret is from the wrong environment, the handler parses JSON before verification, duplicate replay causes repeated side effects, private fulfillment is untested, or refund rollback has no evidence.