Full-Stack Mobile Developer – Crypto & Fiat Exchange / Payments App (Vertical Slice Architecture)

Project Overview We are building a fast, easy-to-use exchange and payment services app that lets users convert between cryptocurrency and fiat currencies (South African Rand and Nigerian Naira), manage virtual and physical cards, and pay bills — all from one platform. We're looking for an experienced mobile/full-stack developer to design and build this app from the ground up, with a strong emphasis on speed, simplicity, and a clean user experience. Core Features Exchange Services - Crypto → Rand (ZAR) - Rand → Crypto - Crypto → Naira (NGN) - Naira → Crypto - Rand → Naira - Naira → Rand - Crypto → Crypto (stablecoin pairs) Card Services - Virtual card issuance - Physical card issuance and management (activation, freeze/unfreeze, top-up) Bill Payments - Integrated bill payment service (utilities, airtime/data, etc.) UX Priorities - Fast transaction processing - Minimal steps to complete an exchange or payment - Clean, intuitive interface suitable for first-time crypto users Technical Requirements - Proven experience building fintech, crypto exchange, or payment apps (please share relevant examples/portfolio) - Must build using **Vertical Slice Architecture** — organizing code by feature/use case rather than technical layer — so features can be developed, tested, and shipped independently - Experience integrating: - Crypto exchange/liquidity APIs and wallet infrastructure - Card issuing platforms (virtual + physical) - Bill payment/aggregator APIs - Local payment rails for South Africa and Nigeria (bank transfers, mobile money, etc.) - Strong understanding of KYC/AML compliance flows and secure handling of financial data - Experience with real-time exchange rate feeds and transaction reconciliation - Backend: robust API design, secure architecture, scalable infrastructure - Frontend: native or cross-platform (React Native/Flutter) — open to developer's recommendation, please justify choice - Solid testing practices (unit/integration tests per vertical slice) Deliverables - Full technical architecture proposal before development begins - iOS and Android app (or cross-platform equivalent) - Admin/backend dashboard for transaction monitoring and support - API documentation - Source code with clean version control (Git) - Post-launch support/bug-fix window What to Include in Your Proposal 1. Relevant past projects (crypto, fintech, or payments apps) with links if available 2. Your experience with vertical slice architecture specifically 3. Recommended tech stack and why 4. Estimated timeline broken into phases/milestones 5. Fixed price or hourly rate, with a breakdown by phase 6. Any experience with South African or Nigerian payment/regulatory environments (a strong plus) Design Reference We have a working interactive prototype (built in React) covering the Home, Exchange, Cards, Bills, and Profile screens, with functioning navigation and mock interactions (live conversion math, freeze/unfreeze card toggle, bill search, etc.). This isn't production code — it has no real backend, payment rails, or data persistence — but it defines the intended UI/UX, user flows, and brand direction (yellow/black, chevron emblem) in detail. We'll share this file with shortlisted candidates so you can see exactly how the app should look, feel, and flow before quoting. Notes This is a phased project — we'd like to start with a working MVP covering core exchange functionality before expanding to cards and bill payments. Developers who can demonstrate a clear milestone-based delivery plan will be prioritized.