Description

This position is strictly open to candidates located in Ukraine.

is looking for a Senior Fullstack Developer (.NET + Flutter) to implement changes in the existing backend and continue the rebuild of the mobile app in Flutter. You will work across the server and mobile sides, from REST APIs to releases in the App Store and Google Play.

This role is a good fit if you can drive tasks independently across the whole stack, care about code quality, and are confident working with payment flows.

About the project

Monyx Wallet (product page) is 's mobile wallet for automated businesses: vending machines, laundromats, car washes and other self-service devices. Users pick a device by number or address, or scan a QR code, and pay from their phone. The app supports prepaid cards for closed-loop systems, promotions and loyalty programs, automatic refunds, branded cards, and an SDK for integration into operators' apps.

Where the project is now. A significant part of Monyx has already been rewritten in Flutter as a standalone plugin with its own repositories. Next, a new standalone Monyx app will be built on top of it in Flutter. Some of the logic still needs to be covered, and the payment and automatic refund flows need further work.

What you will doBackend (.NET)

• Implement changes, new features and bug fixes in the existing backend (C#, .NET / ASP.NET Core).
• Design, extend and document REST APIs for the mobile app (Swagger / OpenAPI).
• Work with relational databases: schemas, efficient queries, migrations.
• Refactor legacy code and improve the performance, reliability and maintainability of services.
• Implement authentication and authorization and handle sensitive and payment data securely.
• Write unit and integration tests and take part in code reviews.
• Support releases, investigate production incidents and perform root cause analysis.

Mobile (Flutter)

• Continue the rebuild of the mobile app in Flutter for Android and iOS.
• Develop new screens, user flows and reusable UI components based on design specifications.
• Integrate the app with backend APIs: error handling, offline states, data caching.
• Implement authentication, onboarding, deep links, push notifications and payment flows.
• Support localization, RTL languages (Hebrew, English) and accessibility requirements.
• Manage state, navigation and app architecture using clean, scalable patterns.
• Prepare builds and publish releases to the App Store and Google Play.

Team and process

• Analyze requirements and user stories, estimate tasks and propose technical solutions.
• Use AI-assisted development tools for design, implementation and testing, carefully reviewing code quality and security.
• Work closely with Product Managers, designers, QA engineers and other developers.
• Take part in Agile ceremonies: sprint planning, backlog refinement, daily stand-ups and retrospectives.
• Maintain technical documentation and help improve engineering processes.
• Share knowledge and mentor middle and junior developers.

Requirements

We are looking for 5+ years of commercial experience building backend services in .NET and cross-platform mobile apps in Flutter. Experience delivering production releases for Android and iOS in Agile teams and a strong focus on code quality, performance and security are also important.

Backend. C# and .NET (.NET 6+ / ASP.NET Core), REST API design, Entity Framework Core and Dapper, SQL (MS SQL Server or PostgreSQL) with query optimization, OAuth 2.0 and JWT, Dependency Injection, Clean / Layered Architecture, SOLID, xUnit / NUnit and Moq.

Mobile. Flutter and Dart (production apps for Android and iOS), state management (Bloc / Riverpod / Provider), REST API integration (Dio / http) and JSON serialization, navigation and deep links, push notifications (Firebase Cloud Messaging), localization, RTL and accessibility, local and secure storage, widget and integration testing.

Tools. Azure DevOps (boards, repos, pipelines), Git and pull request workflow, Swagger / OpenAPI, Firebase (Crashlytics, Analytics, Cloud Messaging), App Store Connect and Google Play Console, CI/CD for backend and mobile.

Platforms and methodologies. Android, iOS, Web API / AWS cloud; Agile and Scrum.

Additional. Code review, application security basics, performance optimization, debugging and root cause analysis, requirements analysis, technical documentation.

Personal qualities

• Ability to work independently across backend and mobile and to manage multiple priorities.
• Ownership and a focus on high-quality, maintainable solutions.
• Effective communication with technical and non-technical stakeholders.
• Proactive problem solving and the ability to make sound architectural decisions.
• Experience in a fast-paced product development environment.
• English at Upper-Intermediate (B2) level.

Nice to have

• Hands-on experience with AI coding assistants (for example Claude Code, GitHub Copilot) for design, implementation, refactoring and test generation, with a critical approach to reviewing generated code.
• Experience in fintech, payments or POS / cashless solutions.
• Native Android (Kotlin) or iOS (Swift) experience for platform channels.
• Microservices, message queues, event-driven architecture.
• Docker and AWS services.
• Mobile test automation (Appium, Flutter integration tests).
• Experience migrating a mobile app to Flutter from native or another framework.

Learn More about Working conditions and format

• Location and format. Work from Ukraine, fully remote.
• Equipment. A work laptop is provided on request.
• Learning. Access to the Juno learning platform.
• Vacation and sick leave. 20 working days of vacation and sick leave.
• Medical insurance. Covers dental care, massages, doctor visits and vaccinations.

About the company and team

(about the company) is a global fintech company that provides an operating system and payment platform for unattended retail: cashless payments, IoT services and management solutions for self-service devices. The company was founded in 2005 and has been listed on Nasdaq (NYAX) since 2022. has more than 500 employees and around 30,000 customers.

You will join the / Weezmo team. Weezmo is an omnichannel solution for retailers that connects customers' online and offline data: email and SMS marketing, customer segmentation, landing pages, digital receipts, analytics and a single API. Weezmo became part of in 2021. In this role you will work on the Monyx Wallet mobile wallet, which was launched in 2015, with its second version released in 2019.