Paybuddy

Overview

Paybuddy is a wallet application where users move money in from a bank account, hold a balance, and pay merchants. The hard part of any payments system is the same: money movement is asynchronous, and the system has to stay correct when confirmations arrive late, twice, or not at all.

Architecture

The system has three parts in a Turborepo monorepo:

• User wallet app — onramp money from a bank, view balance and transaction history, send wallet-to-wallet payments.
• Mock bank server — simulates a real bank's netbanking flow and fires webhooks on transaction completion.
• Merchant portal — accept wallet payments, manage inventory and discounts, and monitor sales.

Webhook-based consistency

The on-ramp flow is deliberately asynchronous:

1. The user initiates a deposit; the wallet records a pending transaction.
2. The bank processes the transfer on its own timeline.
3. The bank calls a webhook on the wallet backend with the result.
4. The webhook handler verifies the payload, marks the transaction complete, and credits the balance atomically.

Balance updates and transaction status changes happen in a single database transaction, so a crash between steps can't create money or lose it. Duplicate webhook deliveries are idempotent — replaying a confirmation doesn't double-credit.

Key decisions

• Eventual consistency by design. The UI shows pending states honestly instead of pretending deposits are instant — the same model real payment systems use.
• Prisma + PostgreSQL for atomic balance mutations and a typed schema shared across apps.
• Docker + CI/CD so the whole multi-app system spins up identically in dev and deploy.

Outcome

A working payments system that demonstrates the patterns production fintech runs on: webhook-driven state machines, idempotent handlers, and atomic ledger updates.