Senior Full-Stack Engineer for Fintech Payment Servicing MVP | TypeScript + PostgreSQL

We are building a financial servicing SaaS platform for a school that offers installment payment plans to students. The platform will manage student onboarding, payment schedules, payments, account servicing, collections, school settlements, reporting, and reconciliation. This is not an early-stage brainstorming project. We already have a detailed Product Specification covering the core data model, account state logic, ledger behavior, payment rules, security requirements, and first development sprint. We are looking for one senior full-stack engineer who can take a defined product specification and build a secure, auditable MVP. Initial stack and architecture: * TypeScript * React / Next.js * Node.js * PostgreSQL * REST APIs * Multi-tenant SaaS architecture * Role-based permissions * Payment processor abstraction * Immutable financial transaction records * Ledger and reconciliation logic * Audit logging * CSV reporting and exports Sprint 1 will focus on: * Project and repository setup * Core PostgreSQL database schema * Authentication and roles * School onboarding * Student account creation * Secure student onboarding links * Account state engine foundation * Ledger foundation * Audit logging * Basic school, student, and internal servicing interfaces Payment processing, identity verification, credit reporting, e-signature, email, and SMS should be built behind clean provider abstractions so vendors can be finalized without forcing major rewrites. We are looking for someone who: * Has shipped production SaaS applications * Has strong TypeScript, Node.js, React, and PostgreSQL experience * Has built payment or financial transaction systems * Understands webhooks and idempotency * Understands immutable financial records and audit trails * Has strong database and API design skills * Writes automated tests * Can work independently from detailed written specifications * Communicates clearly * Knows how to build a lean MVP without overengineering Experience with fintech, payments, lending, accounting systems, loan servicing, or reconciliation systems is strongly preferred. This project will begin with a paid technical test for selected finalists. Strong performance can lead directly into the MVP build, expected to run approximately 1 to 3 months. Please answer these questions in your proposal: 1. Describe one production system you personally built that handled payments, money, balances, or financial transactions. 2. If a payment processor sends the same successful payment webhook three times, how would you prevent three ledger entries from being created? 3. Have you built a multi-tenant SaaS application? Briefly describe the architecture. 4. What is the most data-heavy PostgreSQL system you have personally designed? 5. Which payment platforms or financial APIs have you integrated with? 6. What is your weekly availability during the next 8 weeks? 7. Are you personally doing the development work, or are you applying on behalf of an agency? 8. What would you deliberately not build during the first version of this product? Please include links to relevant prior work when possible. We prefer an individual senior engineer over an agency.