Senior Next.js and React Native Developer for Web, iOS and Android Integration

We are hiring one senior, hands-on Next.js and React Native developer for a focused 14-day implementation and integration phase inside an existing GPU capacity and infrastructure-management application. The total fixed budget is USD 1,000. The application already has an existing web codebase, backend, authentication architecture, approved Figma design and API structure. The selected developer will not build the platform or backend from zero. The developer will: 1. Review the approved Figma source and make limited, client-approved corrections where required. 2. Implement or update the corresponding responsive screens inside the existing Next.js web codebase. 3. Create a focused cross-platform mobile MVP using React Native and Expo for both iOS and Android. 4. Connect the web and mobile journeys to the same existing backend APIs and authentication architecture. 5. Test the completed journeys and provide a clean developer handoff, iOS test build and Android test build. This role requires someone who can work across Figma, responsive web, React Native mobile development and backend integration without changing the approved business model or rebuilding the backend architecture. This is a tightly controlled MVP phase. The fixed budget and timeline do not cover implementing every application screen independently on web, iOS and Android. Before work begins, the client and developer will freeze the priority journeys and exact acceptance scope. EXISTING ENVIRONMENT - Next.js with App Router, React, TypeScript, Tailwind CSS - React Native with Expo for the new mobile MVP - Expo Router or another client-approved React Native navigation pattern - EAS Build configuration for iOS and Android test binaries - Auth0 authentication and protected routes - Existing backend services and documented API contracts - Existing REST or tRPC integration patterns - Git-based repository and branch workflow - Approved Figma source, responsive screens, components, interaction states and assets The successful developer must work inside the current repository and follow its existing architecture. The mobile application may use a dedicated workspace inside the existing repository or another client-approved repository structure, but it must reuse the existing backend contracts, authentication rules, terminology and approved design system. Do not duplicate backend logic, replace Auth0, introduce an unrelated design system or perform a broad rewrite without written approval. PROJECT SCOPE Before work starts, we will agree on a written delivery manifest containing up to 12 combined web-and-mobile work packages. Each package will identify the relevant Figma section and frames, the existing frontend route, whether the package applies to web, mobile or both, the corresponding React Native screen and navigation destination where applicable, the screens and responsive states included, the reusable components required, the existing backend endpoints or API contracts, the loading, empty, error, disabled and success states, and the acceptance criteria. Designs or routes outside the approved manifest are not included in this fixed-price phase. Priority areas may include: authentication, password recovery, OTP and MFA states; KYC onboarding and document-upload interfaces; GPU Compute and Mining capacity listings; GPU and miner capacity-detail pages; hardware image galleries and full-screen image viewing; capacity configuration and reservation review; payment instructions, pending, verification, success and failure states; client dashboard and My Capacity; reservation lists and reservation details; revenue history and revenue-statement presentation; Proof Center evidence and document viewing; account, security, notifications, support, billing, payout or monitoring states; and global loading, empty, error, maintenance and offline states. A shared user journey implemented on web and mobile counts as more work than a web-only route and must be estimated accordingly before the manifest is signed. MOBILE MVP SCOPE The mobile application must use React Native and Expo unless the client approves another approach in writing; run on supported iOS and Android devices from one maintainable cross-platform codebase; reuse the existing backend APIs, authentication rules, roles and data contracts; follow the approved Figma design while applying appropriate iOS and Android interaction patterns; include only the priority journeys listed in the signed delivery manifest; support secure sign-in and sign-out, protected navigation and session restoration; include loading, empty, error, retry and offline handling for the selected journeys; avoid storing API secrets, access tokens or sensitive personal data insecurely on the device; provide an installable iOS build through TestFlight or approved internal distribution; provide an installable Android build through Google Play internal testing or an approved internal APK distribution; and include build configuration, environment instructions and release handoff documentation. The client will provide access to the required Apple Developer, App Store Connect, Google Play Console and Expo accounts if store-connected test distribution is required. The freelancer must never register production accounts in their own name or retain control of signing credentials. REQUIRED EXPERIENCE - At least five years of professional frontend, mobile or full-stack application-development experience - At least three years of strong production experience with React, Next.js and TypeScript - At least two years of production React Native experience, preferably with Expo and EAS Build - Proven Next.js App Router experience - Strong Figma-to-code skills for complex authenticated applications - Experience with Auth0, OAuth, protected routes or an equivalent identity system - Strong experience integrating existing REST or tRPC APIs - Proven experience shipping React Native applications on both iOS and Android - Experience with mobile authentication, deep links, secure token storage, permissions, safe areas, keyboards and platform-specific behaviour - Strong Git, debugging, testing and written-communication skills Experience with SaaS, fintech, KYC, billing, infrastructure, data centres, GPU compute or mining dashboards is preferred. OUT OF SCOPE (unless separately approved in writing) Rebuilding or broadly redesigning the backend; creating new database schemas, financial ledgers or production API endpoints; replacing Auth0 or changing the core architecture; building a KYC provider, payment processor, settlement system or payout engine; building GPU provisioning, usage metering or mining-pool infrastructure; inventing financial calculations or business rules; a broad product or UX redesign; adding routes or journeys outside the agreed manifest; sourcing or using unlicensed hardware images; certifying the entire platform for production launch; rebuilding every web screen as a mobile screen outside the signed manifest; separate native Swift or Kotlin applications; tablet-specific layouts unless listed; push notifications, biometrics, camera workflows, background processing, geolocation or other native-device features unless listed; public App Store or Google Play approval by a guaranteed date; developer-account fees or paid third-party charges; store marketing assets, legal policies, translations or ASO unless listed. CONFIDENTIALITY AND OWNERSHIP This is a confidential commercial application. The public job post intentionally omits the product name, client identities, proprietary architecture, private API details and complete designs. The selected freelancer will receive access after the Upwork contract begins and may be required to sign an NDA. All code, designs, screenshots, data, workflows, business logic and documentation must remain confidential and may not be published, reused, shared or added to a portfolio without written permission. Confidential materials may not be submitted to third-party AI, code-analysis or file-sharing services without written authorization. WORKING METHOD One individual developer must personally complete the work. Agencies and undisclosed subcontracting are not accepted. Communication and payment must remain on Upwork. The developer must provide at least two hours of daily overlap between 10:00 and 18:00 Gulf Standard Time (UTC+4), give daily progress updates, commit regularly, report blockers immediately and remain available for review and defect correction throughout the full 14-day period. BUDGET AND MILESTONES The total fixed budget is USD 1,000 over 14 calendar days. This budget covers only the frozen, priority web-and-mobile MVP manifest. Candidates must not promise full parity across every existing web route within this budget. Milestone 1 - Paid technical trial (USD 100, Days 1-2): one representative vertical slice across web and mobile. Milestone 2 - Shared foundation and priority journeys (USD 250, Days 3-6). Milestone 3 - Reservation and dashboard integration (USD 350, Days 7-10). Milestone 4 - Remaining agreed scope and final QA (USD 300, Days 11-14), including iOS and Android test builds. Only one milestone can be active and funded at a time. Each next milestone is activated after the current one is reviewed and approved. HOW TO APPLY Start your proposal with the word CAPACITY14 and answer every screening question. Generic proposals, agency proposals and proposals that do not explain your personal contribution will be rejected. Do not provide a long company introduction. Show directly relevant evidence, explain what you personally built and confirm that you accept the budget and timeline.