Dymitr S.

Mobile App Developer for React Native & Expo — Top Rated Plus, $100K+ earned, 100% Job Success, 3,600+ hours on Upwork. I build, fix and ship iOS & Android apps end to end. I'm a senior fullstack mobile app developer with 7+ years of experience and 10+ mobile apps shipped to the App Store and Google Play. As a React Native developer and Expo developer I work with founders, startups and product teams who need one reliable engineer: build a new mobile app from scratch, launch an MVP fast, take over a stuck codebase, fix bugs, speed up a slow app, or add complex features like payments, crypto wallets and AI. 🏆 SELECTED MOBILE APPS • HYPE — Solana memecoin trading app: fixed memory leaks and overheating, +70% performance, −85% crash rate, 350,000+ transactions processed • Zypto — crypto wallet app with NFC card, biometric auth and WalletConnect • Spoken — Christian social media app with audio posts, Bible integration and real-time chat • Fields of Peers — React Native dating app on Supabase, live on Google Play • BHVD Labs — NFC check-in app for iOS & Android with PostHog analytics • Trasa Track — fleet GPS tracking mobile app + web admin panel (real-time tracking, routes, dispatcher tasks) • Twinkle — AI mental health app built on OpenAI GPT • Orlik — education app with in-app purchase, live on App Store & Google Play • Lublin BusWidget — offline iOS transit app with Home Screen widgets • Ultimate Fighting Simulator — mobile game for iOS & Android with IAP • Rise or Pay — smart alarm & habit-building iOS app 📍 Based in Poland (CET) — full overlap with EU/UK hours, easy mornings with US East Coast. ━━━━━━━━━━━━━━━━ 📱 MOBILE APP DEVELOPMENT SERVICES ━━━━━━━━━━━━━━━━ • New mobile app from scratch: planning, UI, development, testing, App Store & Google Play release • MVP mobile app development for startups — launch fast on a solid foundation • Cross-platform iOS app and Android app development with React Native, Expo (EAS) or bare CLI • New features, mobile app bug fix and performance work for an existing app • Mobile app maintenance, updates and post-launch support ⚛️ REACT NATIVE & EXPO DEVELOPER • TypeScript, React Native, Expo, EAS Build & EAS Update, React Navigation, Reanimated • Redux Toolkit, Zustand, React Query, offline-first storage (SQLite, MMKV) • Pixel-perfect UI from Figma, animations, dark mode, accessibility, tablet support • Native modules and integrations: camera, maps (Google Maps, Mapbox), GPS, Bluetooth, NFC, biometrics, widgets • Push notifications (FCM, APNs, OneSignal), deep links, authentication (Google, Apple, email, OTP) 🌐 FULL STACK: WEB & BACKEND • Node.js / TypeScript backend, REST API & GraphQL, WebSockets, real-time chat • Firebase (Auth, Firestore, Cloud Functions), Supabase, PostgreSQL • React and Next.js web apps, admin dashboards and SaaS panels that share code with the mobile app • API integration with third-party services, webhooks, analytics (PostHog, Mixpanel, Firebase Analytics) 💳 FINTECH, CRYPTO WALLET & WEB3 APP DEVELOPMENT • Crypto wallet apps, WalletConnect, dApp integration, Solana & EVM, swaps, real-time market data • Fintech app features: payments, transactions, portfolio tracking, KYC flows, secure storage • Stripe, in-app purchases & subscriptions with RevenueCat, paywalls 🤖 AI MOBILE APP DEVELOPMENT • AI chatbots and in-app assistants with streaming responses (OpenAI, Claude, Gemini) • Summarization, voice-to-text, image generation, AI agents and RAG over your data ⚡ MOBILE APP BUG FIX & PERFORMANCE • Crash reduction with Sentry / Crashlytics, memory leak and overheating fixes • Faster startup, smoother lists, lower memory and battery usage • Refactoring legacy React Native code, upgrading React Native & Expo SDK versions 🚀 APP STORE & GOOGLE PLAY RELEASE, CI/CD • Builds, signing, versioning, TestFlight, internal testing tracks • CI/CD with EAS, Fastlane, GitHub Actions • App Store & Google Play submission, review handling and rejections fixed ━━━━━━━━━━━━━━━━ HOW WE WORK ━━━━━━━━━━━━━━━━ 1. Short call: scope, stack, risks, milestones 2. Feature-by-feature delivery with weekly demos and test builds 3. QA, regression and performance pass 4. Store release + post-launch support ⭐ What clients say: "Fantastic developer — highly skilled, excellent communicator", "excellent and professional engineer… very meticulous". 🌍 Industries: fintech, crypto/Web3, healthcare, fitness, education, social & dating, SaaS, e-commerce, marketplaces, booking, logistics & GPS tracking. 👉 Need a mobile app developer? Send me where your app is now (idea / MVP / live app with issues) — I'll reply with a concrete plan and estimate. Mobile App Developer, React Native Developer, Expo Developer, iOS App Developer, Android App Developer, Full Stack Mobile Developer, Mobile App Development, AI Mobile App Development, Crypto Wallet App, Fintech App, Web3, MVP, TypeScript, Node.js, Firebase, Supabase, Stripe, RevenueCat, In-App Purchases, Push Notifications