Senior Full-Stack Mobile Engineer

React Native / Expo — Full-Time or Fractional

The Company

We are partnering with a privately funded, founder-led business developing two software products: a new consumer subscription app and an established B2B operational platform preparing for commercial growth.

The primary product is designed to help dog owners manage important aspects of their dog’s care, development and ongoing wellbeing. The second product was initially created to support complex internal workflows and is now being developed into software that can be sold to other businesses.

Both products are backed by established commercial operations rather than external investment. The founder has previously built and sold businesses across consumer and industrial markets and is now bringing the company’s product and engineering capability in-house.

The Opportunity

We are looking for a hands-on Senior Full-Stack Mobile Engineer to take technical ownership of both products.

The immediate priority is to turn the consumer app’s existing product documentation and early technical work into a reliable, revenue-generating application available through the Apple App Store and Google Play.

Detailed foundational work is already in place, including the proposed architecture and data model, product logic, onboarding and matching approach, health and treatment schedules, training timelines, supporting data, safety rules, user-experience principles and phased release plan.

Some initial development has been completed by a departing part-time contractor using AI-assisted tools. This work has not yet been independently verified and should not be treated as a finished foundation. Your first responsibility will be to assess it honestly, determine what is worth retaining and rebuild anything that does not meet the required standard.

The secondary responsibility is to review and strengthen an existing B2B platform as it moves from an internal operational tool into commercially available software.

There is no technical manager above this position. You will work directly with the founder, take responsibility for delivery and explain technical decisions in clear, practical language.

The company is open to either a permanent full-time engineer or an experienced fractional engineer who can commit enough time to take meaningful ownership. This is a hands-on delivery role rather than a purely advisory engagement.

What You’ll Work On

• Review the existing mobile application, backend, database and AI-assisted code.
• Decide which parts of the current implementation should be retained, refactored or rebuilt.
• Translate the existing product documentation into a practical technical roadmap.
• Define a suitable architecture for the mobile application, backend services and supporting data.
• Build and release the consumer app on both iOS and Android.
• Implement account creation, authentication, onboarding and user-profile management.
• Build matching and recommendation logic based on user answers and supporting data.
• Develop reminders, treatment schedules, training timelines and record-keeping functionality.
• Create logic that responds to dates, user history and changing individual circumstances.
• Implement push notifications, background processes and scheduled events.
• Integrate Apple and Google subscription payments and manage user entitlements.
• Establish appropriate database permissions, privacy controls and application security.
• Introduce automated testing, error monitoring, analytics and reliable release processes.
• Manage App Store and Google Play submission, review and update requirements.
• Review and harden the existing B2B platform ahead of wider commercial use.
• Improve the platform’s reliability, maintainability and security as new customers are onboarded.
• Work closely with a product and brand designer across both products.
• Communicate progress, risks and technical choices regularly to the founder.
• Help shape the company’s longer-term technical direction and future engineering team.

What We’re Looking For

Essential Experience

• Substantial professional experience as a senior full-stack or mobile product engineer.
• Strong experience building cross-platform mobile applications with React Native.
• The ability to work across the mobile interface, backend services, business logic and database.
• Personal involvement in releasing consumer applications on both the Apple App Store and Google Play.
• Experience building apps with paid subscriptions or in-app purchases.
• Live examples of consumer applications that you have helped build and release.
• Experience developing product logic based on dates, user history, rules and changing circumstances.
• Strong TypeScript or JavaScript experience.
• Experience designing and working with relational databases.
• The ability to assess an unfamiliar or incomplete codebase and determine what should be kept, improved or rebuilt.
• Confidence working independently without a technical manager.
• Experience taking a product from an early stage through to a production release.
• An understanding of mobile security, user privacy and reliable data handling.
• The ability to explain technical decisions clearly to non-technical stakeholders.
• The willingness to collaborate in person in Barcelona or Málaga, particularly during the early stages.

Particularly Relevant Experience

• React Native and Expo in production environments.
• Expo Application Services for building, submitting and updating mobile applications.
• Supabase, PostgreSQL or comparable backend platforms.
• Authentication, storage and row-level security.
• RevenueCat, StoreKit, Google Play Billing or comparable subscription-management tools.
• Push notifications, scheduled reminders and background processes.
• Consumer health, wellbeing, pet-care or lifestyle applications.
• Rules engines, recommendation systems or personalised product journeys.
• Mobile analytics, crash reporting and application monitoring.
• Automated mobile testing and continuous delivery.
• Reviewing or improving software created with AI-assisted development tools.
• Supporting an existing B2B software platform while developing a new consumer product.

You do not need direct experience with every technology listed above. Evidence that you have personally built, released and supported complete consumer applications is more important than matching every keyword.

How You Work

• You take ownership of outcomes rather than waiting for individual tickets.
• You are comfortable working in a founder-led environment without heavy processes.
• You move quickly while maintaining an appropriate standard of reliability and security.
• You assess existing work objectively instead of automatically keeping or replacing it.
• You raise concerns and alternative approaches early rather than changing direction without alignment.
• You communicate progress regularly and do not disappear into development for long periods.
• You explain technical subjects in language that non-technical colleagues can understand.
• You consider every product decision from the user’s perspective.
• You understand that many users will not be technically confident and design accordingly.
• You can turn extensive product thinking and documentation into a focused, achievable build plan.
• You remain hands-on across coding, testing, debugging, deployment and production support.

Current Technical Environment

The existing work is understood to include:

• TypeScript
• React Native
• Expo
• Supabase
• PostgreSQL
• Vercel

The current implementation has not yet been fully verified, and the technology stack remains open to recommendation.

The company is not looking for someone to replace the stack simply based on personal preference. The priority is to review what exists, understand the product requirements and recommend the most practical architecture for launching and supporting the products successfully.

Location and Working Model

The role can be based in Barcelona or Málaga, with the final working arrangement agreed with the successful candidate.

The founder values working alongside the people building the products and wants regular in-person collaboration, particularly during the initial product and architectural stages. This is therefore not intended to be a fully remote position.

For a fractional engagement, the exact time commitment and working pattern can be discussed. However, the person must have sufficient availability to maintain momentum, communicate regularly and remain accountable for delivery.

Portfolio Requirement

Please provide links to live consumer applications that you have personally helped build and release.

The most relevant examples will be applications that:

• Are currently available on iOS or Android, ideally both.
• Have real users and are actively maintained.
• Include paid subscriptions or in-app purchases.
• Contain meaningful backend logic rather than functioning primarily as content or presentation layers.
• Demonstrate a clear, accessible and considered user experience.

Candidates should be prepared to explain their individual contribution to each product. Live application examples will be considered as important as the CV.

Why Join?

• Become the first in-house technical owner across two commercially focused products.
• Take a well-developed consumer concept through engineering, launch and revenue generation.
• Build a product intended for real users rather than an internal prototype.
• Make meaningful architectural and product decisions without unnecessary layers of approval.
• Work directly with a commercially experienced founder.
• Collaborate closely with a product and brand designer.
• Influence future engineering standards, technical direction and team growth.
• Work on both a new consumer application and an established B2B platform.
• Join a business funded through existing commercial activity rather than dependent on external investment.

Interested?

If you are a senior engineer who has personally built and released consumer subscription apps and would enjoy taking genuine ownership of a product from an early stage, we would be happy to speak with you.

Apply directly or contact [email protected] for a confidential conversation. Please include links to relevant live applications with your application.