Cross-Border Bill Payment and Top-Up Platform
We built a LINE Mini App for Taiwan customers to pay Indonesian utilities and buy digital goods. Its backend treats payment and fulfillment as a verifiable state machine. It coordinates five suppliers and a Taiwan payment gateway without double charges, lost orders, or manual supplier-failure recovery.
ESA processes real-money transactions between Taiwan customers and Indonesian suppliers. Each checkout touches ECPay, one or more suppliers, and an asynchronous webhook. Any step can time out, return ambiguously, or succeed silently. The system had to prevent duplicate charges and fulfillment, fall back when suppliers fail, compare IDR and NTD costs, integrate five provider contracts, and retain a complete order record.
Cross-Border Bill Payment and Top-Up Platform
NestJS, Prisma, and PostgreSQL form one transactional core for the LINE Mini App and admin dashboard. Payments move PENDING → PAID → SUCCESS or FAILED. Items have separate lifecycles. A provider layer routes fulfillment through one contract. ECPay returns signed webhooks. A 10-minute cron finds stuck payments and alerts operators. A 12-hour cron syncs catalogs with per-supplier isolation.
Payments use a state machine, making idempotency and recovery decidable. A provider abstraction isolates supplier details from payment logic. Suppliers are ranked by effective cost and fall back automatically. One Prisma transaction covers payment, items, history, and promo usage. Non-reversible effects wait until commit. Structured JSON stores provider requests, responses, and schema differences.
State inspection short-circuits duplicate webhook and retry processing. ECPay callbacks pass CheckMacValue (AES-128-CBC) validation before state changes. Checkout returns immediately, while fulfillment runs asynchronously. Stored exchange rates drive IDR and NTD cost comparison. Payment history, item records, and provider exchanges reconstruct every order. Bounded concurrency protects supplier APIs during catalog sync.
Runs in production behind a LINE Mini App for Taiwan customers buying Indonesian digital products.
State-machine lifecycles and idempotency prevent duplicate charges and fulfillment.
Five-supplier fallback protects customer experience during supplier outages.
Reconciliation finds stuck payments within minutes.
New suppliers integrate without changing core payment logic.
Persisted state and provider history reconstruct every order.
Idempotency, atomic writes, deferred side effects, and state machines prevent duplicate charges and fulfillment by design.
Supplier failure triggers automatic, cost-aware fallback.
Five suppliers with different auth and payload contracts sit behind one interface. The business core stays stable as integrations change.
Continuous reconciliation recovers from missed webhooks and provider failures.
Money-moving systems depend on asynchronous webhooks that can be delayed or dropped. Reconciliation enforces correctness after the request.
Applicable to payment platforms and marketplaces that orchestrate multiple providers. It fits cross-border commerce and money-moving systems that require idempotency, failover, and auditability, including LINE Mini App products.
We specialize in dedicated team for fintech companies. If you're facing challenges like the ones we solved for ESA, let's talk.
