Mobile • E-Commerce • Payments

E-Commerce Mobile App

A production-grade mobile commerce system built around correct order state, payment reliability, webhook reconciliation, and predictable checkout behavior under failures.

Checkout Reliability Idempotency Webhooks Fraud Signals Performance

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Record Summary

A real-world payments + state machine engineering record (NDA-safe).

Scope

Catalog → cart → checkout → payment → order lifecycle → refunds and cancellations.

Risk

Duplicate charges, race conditions, webhook delays, and inconsistent client-side order state.

Outcome

Stable checkout flows with server-authoritative state and reconciliation guarantees.

Problem What broke

Common commerce failures.

Payment success shown to user while webhook arrives late or fails.
Retrying checkout caused duplicate intents/charges.
Mobile network instability produced state divergence (client vs server).
Refund and cancellation rules were inconsistent across providers.

Fix Engineering

How it was resolved.

Server-authoritative order state machine (no client-side “truth”).
Idempotency keys for every payment attempt and order mutation.
Webhook reconciliation pipeline with retries, signatures, and auditing.
Consistent refund/cancel API and provider adapters.

Implementation Highlights

Elite without buzzwords.

Order State Machine

Correctness

Explicit states: Created → PaymentPending → Paid → Fulfillment → Completed / Refunded / Cancelled.

Payment Idempotency

No Duplicates

Every attempt carries an idempotency token across client and backend, preventing double charges.

Webhook Verification

Signed

Signature verification + replay protection + strict event validation before state transitions.

Reconciliation & Audit

Reliable

Late webhooks, provider outages, and retries are handled with safe reprocessing and audit trails.

Need a stable checkout under real-world failures?

Payments, webhooks, and order correctness engineered for reliability — not luck.

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