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Payments Checklist for AI-Built Apps

One-time and recurring charges

When you vibe code payments with tools like Cursor, Lovable, Bolt, v0, or Claude Code, the generated code often works in development but misses critical production requirements. This checklist helps you catch what AI missed before you ship.

Danger Zone

critical risk

A billing bug doesn't just lose data — it loses real money and real trust at the same time

Adding payments looks like dropping in a Stripe widget. But behind that widget is a maze of things that need to work perfectly: what happens when someone upgrades mid-month, how to retry failed cards without annoying people, calculating tax for different countries, handling refunds and disputes, and making sure your app and your payment provider agree on who's paid and who hasn't. Every billing bug is either lost revenue or an angry customer.

Failure scenario

You launch a SaaS with monthly billing. Everything's great for a few months. Then a customer downgrades their plan mid-cycle and gets charged full price anyway. You never built the logic for partial refunds. Now you have 200 support emails, a public complaint thread, and your payment provider is flagging you for too many disputes.

Common mistakes

  • Processing the same payment notification twice, causing double charges
  • No logic for what happens when someone changes plan mid-month (they get overcharged)
  • Not tagging payments with unique IDs, so retries create duplicate charges
  • Accidentally logging credit card numbers or payment secrets in error reports
  • When a card fails, immediately canceling instead of retrying a few times over a few weeks

Time to break: 1-3 months before the first billing dispute becomes a real problem

How are you building this?

Showing what to check when using a managed service

Audit Prompts

Copy these into your AI coding assistant to check your implementation.

Are payment notifications handled correctly?
reliability
Look at how we handle notifications (webhooks) from our payment provider like Stripe or Paddle. Check: Do we verify each notification is actually from the provider (not faked)? If the same notification arrives twice, does it only get processed once? Are we listening for all the important events — successful payments, failed payments, subscription changes, cancellations? Is there logging so we can investigate when something goes wrong?

Payment notifications are how your app knows someone paid. If one gets missed, a paying customer loses access. If one gets processed twice, someone gets charged twice.

Does your app agree with your payment provider about who's paid?
cost
Check that our app and our payment provider (Stripe, Paddle, etc.) always agree on subscription status. If someone upgrades, downgrades, or cancels through the provider's dashboard (not just our UI), does our app update? Is there a way to detect when they get out of sync? Are we using the provider's built-in proration (partial billing) instead of trying to calculate it ourselves?

If your database says someone is paying but Stripe says they canceled, either they're getting free access or you're losing track of revenue.

Is payment data kept secure?
security
Check our payment setup for basic security. Are secret API keys only used on the server (never in browser code)? Do credit card numbers show up anywhere in our logs or error tracking? Are we using the payment provider's pre-built payment forms (not collecting card numbers ourselves)? Are test and live modes properly separated?

Handling credit card data incorrectly can result in fines and losing the ability to accept payments entirely. Using the provider's payment forms keeps you safe.

What happens when a payment fails?
cost
Check what happens when someone's card gets declined. Is there an automatic retry sequence (trying again in a few days, then a week)? Does the user get an email telling them to update their card? Do they lose access immediately or get a grace period? Is there a page where they can easily update their payment method?

Failed cards cause 20-40% of subscription cancellations. The difference between "immediately cancel" and "retry with a friendly email" can be thousands of dollars in saved revenue.

Checklist

0/10 completed

Smart Move

Use a service

Handling real money means legal requirements, fraud risk, and hundreds of edge cases across currencies, taxes, and payment methods. Nobody should build their own payment processing. The only question is which service to use.

Stripe

The industry standard — handles one-time payments, subscriptions, invoicing, tax, and fraud detection

No monthly fee — 2.9% + 30 cents per transaction

Paddle

Handles global tax and compliance for you — you never think about VAT or sales tax

5% + 50 cents per transaction (but no tax headaches)

LemonSqueezy

Simpler alternative to Paddle, popular with solo founders and indie products

5% + 50 cents per transaction

Tradeoffs

Transaction fees add up as you grow, and you're subject to the provider's rules on disputes and payouts. Stripe gives more control but more responsibility; Paddle/Lemon handle taxes automatically but take a bigger cut.

Did you know?

Each payment dispute costs an average of $190 in fees, penalties, and lost product — and if more than 1% of your payments get disputed, your payment provider can shut down your account.

Source: Chargebacks911 2024 Industry Report

Related Checks

🔐Authentication

Sign up, log in, password reset, 2FA

📤Data Export

Let users download their data

🩺Monitoring

Error tracking and observability