Case study
Crypto-to-Fiat Payment Gateway
Designed and implemented the backend and operational workflow for a crypto-to-fiat payment gateway, including idempotency, transaction boundaries, and reconciliation.
Role
Technical Architect
Technology
- Node.js
- REST APIs
- Transaction State
- Reconciliation
- Nginx
Context
A crypto-to-fiat gateway had to coordinate blockchain events with conventional fiat payment workflows and operational review.
Problem
Retries, duplicate callbacks, asynchronous settlement, and uncertain external responses make a payment flow unsafe when it is modelled as one simple request.
Constraints
The system handled sensitive transaction state. Public materials do not establish regulated-production authorization, payment volume, or a reliability SLO.
My role and ownership
I shaped the backend service boundaries, transaction-state handling, and operational infrastructure with a four-person engineering team.
Architecture
Request → idempotency key → persisted intent → external crypto/fiat adapters → reconciliation state. Each boundary returned a durable state transition instead of assuming that a remote response was final.
Key decisions and trade-offs
Durable state and reconciliation add bookkeeping, but they make retries and manual review explainable. The design favoured explicit recovery over pretending external systems were synchronous.
Failure modes and safeguards
Duplicate requests, delayed callbacks, and mismatched settlement states were treated as recoverable workflow states. Idempotency and reconciliation were the safeguards; no five-nines claim is made.
Implementation scope
Outcomes
Implementation scope covered backend services, transaction-state handling, reconciliation, and the supporting operational workflow.
Evidence boundary
The public case study documents design ownership and safeguards. Provider names, transaction volumes, compliance details, and production evidence remain confidential.