Flutter Developer — Travel Connectivity App (iOS + Android), Budget-Friendly, Milestones

ENGAGEMENT: Fixed price, milestone-based, acceptance-driven payments through Upwork escrow. We are a lean, early-stage company looking for a competitive, budget-friendly quotation and strong value for money. (See the budget note at the end of this post.) TIMELINE: We do not impose a timeline — you propose your own delivery schedule, milestone by milestone, in your application. Speed matters to us: the faster you can deliver at full quality, the stronger your application. If you can realistically deliver in one month, tell us and show us how. Your proposed timeline becomes a commitment in the contract, so make it honest — unrealistic promises will count against you at screening. ABOUT US AND THE PROJECT We are a Japan-based connectivity company selling in the USA and in Japan. Customers buy our portable WiFi hotspot devices (cloud SIM routers) and use our app to link their device, purchase data packages, and monitor usage. The SAME app is also our eSIM store: customers with no device at all buy travel eSIMs for their smartphones and recharge them. Both functions — WiFi device recharge AND eSIM sales — are part of this contract from day one. Further commercial details are shared with shortlisted candidates under NDA. This is a production application for paying customers in two countries — it must be complete, reliable, and professionally finished on day one. WE WELCOME APPLICANTS FROM ANYWHERE IN THE WORLD. Selection is based on demonstrated work quality first and price competitiveness second — the strongest proposal at the best price wins, regardless of location. We work asynchronously (we are in Japan, JST), so your timezone is not a factor. REFERENCE APPS — WHAT WE EXPECT The category is defined by the GlocalMe app (App Store / Google Play) and the RoamWiFi app. Download at least one before applying. These references define the expected standard: device linking, destination-based plan store, purchase flow, eSIM purchase and installation, live balance monitoring, and usage management — executed at commercial quality. Your proposal should reflect that you have studied how these apps work. PLATFORM ARCHITECTURE — TWO BRANDED APPS, ONE SYSTEM We operate two brands: Brand A (USA/global market, English-first, built and launched under this contract with full functionality) and Brand B (Japan market, Japanese-first, same functionality customized for Japan — a later, separately priced phase). You will build one codebase and one backend architected from day one to produce both branded apps as build flavors (separate names, icons, themes, catalogs, and per-market feature modules) without rework. Brand names are disclosed under NDA. Deliver Brand A well and the Brand B phase and ongoing maintenance are natural follow-on work with us. REQUIRED FUNCTIONALITY — ALL PART OF THIS CONTRACT A. Accounts and devices 1. Account creation and login: email, Apple Sign-In, Google Sign-In 2. Device linking by QR code scan (camera) or serial number entry B. Store and checkout (serves BOTH product types) 3. Plan catalog organized by destination — plans, prices, and validity fully managed from the admin panel, never hardcoded; supporting fixed-data packages and per-day passes, for both WiFi device recharges and eSIMs 4. Checkout: Stripe with cards, Apple Pay, Google Pay; receipts; refunds via admin panel. Checkout must be architected so Japanese payment methods (konbini, PayPay) can be added in the Japan phase without restructuring. If you recommend a processor better suited to US+Japan than Stripe, justify it. C. WiFi device recharge 5. Purchase of data packages provisioned to the linked device via our supplier's API 6. Balance and usage screen: remaining data, validity countdown, usage history 7. Push notifications (Firebase Cloud Messaging): 80% usage and pre-expiry alerts D. eSIM sales and recharge 8. eSIM storefront by destination: purchase → instant delivery of the eSIM profile with one-tap install on iOS, the equivalent flow on Android, QR code fallback, and email backup of the activation details 9. Top-up/recharge of previously purchased eSIMs from order history 10. Device eSIM-compatibility checker before purchase E. General 11. Order history covering both product types 12. Offline caching of device credentials, purchased plan details, and eSIM activation codes 13. Support section: FAQ + contact channel 14. Full English and Japanese interface with complete parity — fully internationalized (i18n) architecture: all text in translation files, correct currency (USD/JPY) and date formats, automatic device-language detection with manual override, and the ability to add future languages with translation files only 15. Web-based admin panel: manage plans/prices per brand, market, and product type; look up customers, devices, and eSIM orders; view orders; issue credits and refunds 16. Store launch: preparation of both store listings (we provide brand assets), submission under OUR developer accounts, and handling reviewer feedback through to approval on BOTH stores 17. Integration with our data supplier's REST API: provisioning packages to devices, eSIM profile purchase and delivery, balance/usage queries, usage webhooks. Documentation and sandbox provided under NDA. All supplier calls are server-side; the app communicates only with our backend. REQUIRED TECHNOLOGY STACK Flutter (Dart), single codebase for iOS, Android, and a web build (React Native only with written justification). Backend: Node.js or Python with REST API and PostgreSQL — propose and justify. Firebase Cloud Messaging. Deployment to our cloud account (AWS or GCP). All source code pushed continuously to OUR Git repository from day one; we own all code and IP in full. MILESTONES AND PAYMENT TERMS — ONE CONTRACT, ALL FUNCTIONALITY Every milestone is funded into Upwork escrow and released only upon our acceptance of a working, testable deliverable — never for time or progress reports. A milestone is not acceptable if its code is not in our repository. Escrow means your payment is secured before each milestone begins — this is a low-risk engagement for a professional who delivers. M1 (10%) — UI designs for ALL screens approved (EN + JP), covering device recharge AND eSIM flows M2 (20%) — Working build on our own iPhone and Android: accounts, device linking, full catalog (both product types), and balance screens functioning against the supplier sandbox M3 (25%) — End-to-end purchases working on our devices for BOTH products: (a) pay → data package provisioned to WiFi device → balance updates → notification fires; (b) pay → eSIM delivered → installed on a real iPhone and a real Android phone M4 (40%) — FINAL DELIVERY: the complete app — device recharge AND eSIM store — approved and LIVE on both the App Store and Google Play, bilingual QA complete on real devices, admin panel operational, all code and deployment documentation delivered M5 (5%) — End of 3-week post-launch warranty period (bug fixes included) We test each milestone within 5 business days and either accept or return a written defect list. The percentages apply to the total budget agreed at screening. There is no separate later milestone for eSIM functionality — it is inside this scope; quote accordingly. YOUR APPLICATION MUST INCLUDE ALL OF THE FOLLOWING — incomplete applications will not be reviewed: 1. Links to app(s) YOU built that are LIVE today on BOTH the Apple App Store and Google Play. We will download and test them. The work must be functioning and relevant to this industry or close to it: telecom, eSIM/top-up, travel, e-commerce, fintech/payments, or subscriptions. Portfolio PDFs are not a substitute for store links. 2. A brief description of a payment integration you have built (Stripe or similar). 3. A brief description of a third-party REST API integration with webhooks you have built. 4. Written answer: "A customer pays, but the supplier's provisioning API call fails. Walk us through exactly how your system handles this." (Weighted heavily.) 5. Written answer: "Why can this app use Stripe instead of Apple In-App Purchase, and what would you write in the App Review notes to pass review?" 6. Your experience with i18n/Japanese text support, with eSIM delivery/installation flows if any, and with multi-flavor or white-label builds. 7. An indicative estimate for the FULL scope above (both product types), broken down against milestones M1–M5, AND your proposed timeline for each milestone with a total delivery date. Faster realistic timelines are viewed favorably. This estimate is not a final commitment — the final quotation and schedule will be agreed during screening, after you receive the complete scope document under NDA. Budget-friendly, value-for-money estimates will be prioritized for shortlisting. 8. Your start date and weekly hours you will dedicate to this project. Shortlisted candidates sign an NDA and receive the complete scope document, brand identities, and supplier API documentation before the final quotation discussion. You will work directly with the founder — clear, plain-English communication is a requirement of this job. *** NOTE ON THE POSTED BUDGET: The $1,000 shown on this job is a placeholder only — it is NOT the project budget. Upwork requires a figure to publish a fixed-price job. The real total budget and the milestone amounts will be discussed in detail with shortlisted candidates during the screening process, and each milestone will be funded into Upwork escrow when the project starts. Please base your indicative estimate (application item 7) on the full scope described above, not on the placeholder figure. ***