Secure One-Time Payment Gateway Build

The goal is to deliver a full-stack payment service that cleanly handles one-time transactions while supporting Credit/Debit Cards, Digital Wallets, and direct Bank Transfers. I need an end-to-end solution that exposes a well-documented REST or GraphQL API, encrypts every sensitive data flow, and can be dropped into a wider micro-service environment without friction.

Core scope
• Process single-charge requests, capture funds, issue refunds, and return real-time status callbacks.
• Connect to the major card networks, popular wallet providers (Apple Pay, Google Pay, etc.), and standard bank transfer rails.
• Apply strong encryption—at rest and in transit—so PANs, tokens, and webhooks remain protected.

Preferred tech
I am flexible on language and framework; proven stacks such as Node.js/TypeScript, Go, Java/Kotlin, or Python/FastAPI are all acceptable, provided you can demonstrate low-latency performance and clean, testable code.

Deliverables
1. Source code with clear build instructions (Dockerfile or similar).
2. API reference (OpenAPI/Swagger) covering charge, refund, and status endpoints.
3. Database schema and encryption approach.
4. Unit & integration tests showing successful card, wallet, and bank transfer flows.
5. Brief deployment guide for staging and production.

Acceptance criteria
• A single transaction from request to gateway response completes in <2 s under moderate load.
• All cardholder data encrypted with strong ciphers (e.g., AES-256-GCM).
• Endpoints return consistent, valid JSON with idempotency keys.
• Test suite passes on GitHub Actions (or similar CI).

If you already have PCI-DSS experience, please mention it; otherwise show how you will meet its minimum encryption requirements. I will be available for quick technical clarifications throughout the build and can provide test credentials for each payment rail once the skeleton service is running.