Stripe Checkout Flow

PROJECT CONTEXT:
I am building a web app and need users to pay via Stripe (one-time or subscription).

GOAL:
Implement a real Stripe checkout flow with server-side sessions, webhook confirmation, and visible payment status.

REQUIREMENTS:
- Server-created Stripe Checkout session (never expose secret keys to the client)
- Success and cancel pages
- Webhook or verification that confirms payment server-side
- Payment/order record stored in the database
- Paid state visibly reflected in the UI
- Test mode end-to-end with Stripe test cards

CONSTRAINTS:
- Never trust the frontend to declare a payment successful
- Never hardcode price amounts on the client
- Handle canceled and failed payments explicitly

DEFINITION OF DONE:
- Clicking pay opens a real Stripe checkout
- A test card completes payment successfully
- Payment status is confirmed server-side and stored
- The UI reflects paid status after checkout
- Cancel path returns the user cleanly without a fake success

COMMON FAILURES TO AVOID:
- A 'Pay' button that redirects to a success page without ever calling Stripe
- Payment status set from the client success redirect instead of server verification
- Secret key exposed in frontend code
- No handling of canceled or failed payments
- Amounts defined on the client where users can edit them