Senior Full-Stack Developer for E-commerce Payment & Checkout Optimization

Prototype Project: Payment Webhook & Duplicate Protection

Goal
Improve the reliability of our payment system by preventing duplicate processing and strengthening webhook handling.

Tasks
1. Review Current Payment Flow
Provide a short summary (1 page max) explaining:
- How checkout works
- How payments are confirmed
- How webhooks are processed
- Where duplicate or failure risks exist

2. Add Idempotency / Duplicate Protection
Ensure that:
- Repeated webhooks do not update the same order twice
- Replayed events do not create duplicate records
- Each payment event is processed only once
Use gateway event id / transaction id / payment intent id.

3. Improve Webhook Security & Logging
- Verify webhook authenticity (if supported)
- Return correct HTTP status codes
- Add useful logs (event id, order id, status change, errors)
no sensitive data in logs.

4. Provide Test Evidence
Show proof that the fix works (screenshots, logs, test script, or short report).

Deliverables
- Clean code committed
- Short documentation
- Test proof

Acceptance
Pass if:
- No duplicate processing
- Webhooks are verified
- Code is clean and stable
- Documentation is clear

Fail if:
- No real idempotency
- No explanation
- Breaks existing flow