B2B FinTech Invoicing Platform

Solo

Delivery

14+

DB tables

Web + Mobile

Platforms

The Challenge

An Australian fintech startup needed a production invoicing platform with cryptographic document integrity, multi-stage tax compliance validation, accounting ERP integration, and both web and mobile interfaces — delivered under a structured milestone contract with formal acceptance gates.

The Solution

Designed the complete system architecture and delivered as solo technical lead. Built a modular Node.js backend with DDD-style boundaries, PostgreSQL multi-tenant database (14+ tables), deterministic document canonicalization (JCS + SHA-256), Ed25519 digital signing, and a 5-stage validation pipeline for Australian GST compliance.

Integrated with Xero accounting via OAuth for invoice synchronization with create/update/read-back parity. Built a React admin dashboard with TanStack Query and a React Native mobile app with Expo SDK 54.

Created all technical documentation from scratch including the Product Requirements Document (PRD) and Technical Annex. Delivered under a structured milestone contract (M0-M5) with formal acceptance at each gate.

Results

Solo delivery of complete platform: backend + web admin + mobile app

Solo technical delivery under structured milestone contract

Cryptographic document signing: JCS + SHA-256 + Ed25519

5-stage AU-GST validation pipeline

Multi-tenant PostgreSQL with 14+ tables

Xero ERP OAuth integration

CI/CD with Jest, ESLint, GitHub Actions, CycloneDX SBOM

Complete PRD + Technical Annex authored from scratch

Tech Stack

Node.js 20ExpressPostgreSQL 16SequelizeReact 18ViteTanStack QueryReact NativeExpo SDK 54JestGitHub Actions

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