Senior Full-Stack Engineer - Escrow & Anti-Fraud PropTech (Node.js/PostGIS/Retool/Flutter)

PropTech Full-Stack Architect Needed: High-security land reservation engine for the West African diaspora. Public budget is set to $5,000 to filter for senior talent—100% complete Figma designs, translation sheets, and screen assets are frozen and ready for day-one handoff. There is zero UI/UX discovery or layout guesswork required. We need an expert engineer to focus entirely on building the type-safe Node.js backend, precision PostGIS geometric validation queries to prevent property fraud, an internal Retool dashboard, and compiling the production Flutter client. Job Description We are building a hyper-secure, low-bandwidth, multilingual peer-to-peer land reservation platform explicitly designed to eliminate real estate fraud for the Guinean Diaspora. To minimize regulatory liability and maximize trust, our platform acts purely as an orchestration layer. We do not hold client deposits directly; instead, we leverage third-party payment gateways (Flutterwave / CinetPay) to handle cross-border escrow and automate payouts to local rails in Guinea (Orange Money, MTN MoMo, and local banks). Because the app operates over spotty network connections inside Guinea, our architecture relies strictly on heavy backend-driven business logic rather than client-side processing. Communication is kept lightweight by bypassing custom chat infrastructures in favor of a premium mobile modal sheet that hands off context seamlessly to WhatsApp. Physical property validation is highlighted via an administrative verification badge system controlled directly by our operational field agents via Retool. We need a Senior Full-Stack Engineer to build this type-safe backend engine, manage the spatial database, integrate African payment gateways, and implement these clean, low-overhead mobile UX patterns. ________________________________________ 📅 Project Scope & Asset Readiness This project is structured as a fixed-price contract divided into clear, verifiable deliverables. 🚀 Zero UI Discovery Time Required: 100% complete Figma files, structural translation sheets, and front-end screen assets are finalized and ready to hand over on day one. The mobile user flows, screen interactions, and design guidelines are fully locked down—there is zero layout guesswork or design discovery required. The focus is purely on infrastructure deployment and engineering execution. • Milestone 1: Backend API Setup & Core Architecture (Auth, Routes, AWS S3/Spaces integration). • Milestone 2: PostGIS & Spatial Queries (Anti-overlap geometry validation engine). • Milestone 3: Fintech & Retool Integration (Webhook handlers, split payments, operational admin panel). • Milestone 4: Flutter UI Layout Implementation, WhatsApp Deep-Linking & Handoff. 📌 Phase 1 Architecture Note: While this contract outlines the full framework, we prioritize spatial integrity and deep-linking stability. If structural integration challenges arise during technical scoping, we are prepared to adjust the immediate roadmap to focus exclusively on launching a highly robust Phase 1 core (Verified spatial listings, boundary collision checks, and manual WhatsApp transaction handoff). ________________________________________ 🛠 Technical Architecture & Core Components • Application Server Layer: Node.js (Express or NestJS) in TypeScript, exposing a lightweight, stateless, token-authenticated RESTful API optimized for low-bandwidth environments. • Database Infrastructure: PostgreSQL 16+ with PostGIS for complex geometric multi-point polygon calculations to map land boundaries and prevent overlapping claims. • Fintech & Escrow Integrations: Flutterwave and/or CinetPay to manage cross-border collections, escrow custody, and local payout automation. • Internal Operations Framework: Retool (Cloud/Self-Hosted) serving as the master administrative dashboard for transaction compliance and manual verification triggers. • Storage Repository: AWS S3 (or DigitalOcean Spaces) for secure, private land title and asset preservation. • Mobile Client Integration: Flutter (EN/FR interface) mapped precisely to our finalized design files. ________________________________________ 🎯 Key Responsibilities 🛡️ Anti-Fraud Spatial Engineering • Write precise PostGIS queries and multi-point polygon calculations to validate geographic land boundaries. • Ensure no new property submissions overlap with existing coordinates in the system (ST_Intersects, ST_Overlaps). 💳 Fintech & Escrow Orchestration • Integrate African payment gateways (Flutterwave/CinetPay) to manage complex escrow holding states. • Build robust webhook handlers to process split payment states and programmatically trigger payouts to local mobile money rails. ⚙️ Admin Verification Badge System • Implement a manual action toggle inside Retool for field agents to verify a property's validity. • Wire this backend toggle to instantly render a visual trust marker/badge on the Flutter mobile client. 📱 Low-Overhead Mobile UX & WhatsApp Deep-Linking • Implement a clean, premium frontend transition/confirmation modal sheet in Flutter strictly adhering to the complete Figma specifications. • Configure a high-visibility, primary action button: "Connect via WhatsApp" / "Contacter via WhatsApp" integrating standard WhatsApp branding cues into our app's palette. • Embed a compact pre-filled summary text card containing the specific Land Plot ID, location, and price into the WhatsApp launch deep-link. ________________________________________ 💪 Required Experience • Expert TypeScript & Node.js: Production-level experience building stateless, token-authenticated APIs (NestJS or highly structured Express). • Advanced PostGIS & Postgres 16+: Deep knowledge of geographic coordinate systems (SRID 4326), multi-point polygon calculations, and spatial query optimization. • Retool Mastery: Experience building secure internal tools with direct read/write database workflows, action toggles, and API integrations. • Flutter Frontend Implementation: Ability to build premium, highly polished UI components, modals, visual trust markers, and deep-linking integrations. • African Fintech Integration: Deep, practical experience integrating Flutterwave, CinetPay, or similar gateways with local mobile money (Orange Money/MTN MoMo). • Language: Professional working proficiency in English; French literacy is a major plus due to local market constraints. ________________________________________ 📝 Application Requirements & Screening Questions To verify you have thoroughly reviewed our structural specification and possess the senior architectural experience required, please answer the following questions with your proposal. Generic, automated, or copy-pasted responses will be immediately disqualified. 1. The Infrastructure Estimation Check: Factoring in that 100% complete Figma designs and translation specs are handed over on day one (removing all layout discovery buffers), please provide a realistic, professional estimate of the total hours required to build this system, broken down individually by our 4 target layers: o Layer A: Node.js TypeScript API, Auth, & AWS S3 Core Architecture o Layer B: PostGIS Polygon Collision Validation Engine o Layer C: Fintech Escrow Webhooks & Multi-currency Payout Orchestration o Layer D: Flutter UI Components & Retool Master Admin Framework 2. AI-Accelerated Workflow Strategy: We want to build fast without sacrificing architectural safety. How do you leverage AI tools (e.g., Cursor, GitHub Copilot, custom LLM pipelines) in your current development workflow to dramatically compress project timelines? Specifically, how will you ensure your AI workflows don't introduce vulnerabilities or spatial/financial logic bugs? 3. Please provide a brief example of a PostGIS query or structural workflow you have previously written to handle spatial coordinate checking or to prevent geographic boundary overlap. 4. Briefly highlight your direct experience working with African financial rails (Flutterwave, CinetPay, Orange Money, or MTN MoMo).