B2B FinTech Invoicing Platform
Architecture at a glance
Invoice integrity & compliance (conceptual)
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
Tech Stack
Related reading
How this kind of system is designed and cost-optimized in practice—written for technical founders and engineering leads.
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