Senior Full-Stack Product Engineer - Next.js React Native Design Systems & Quality Remote within Poland B2B 160–300 PLN/hour + VAT 20–40 hours/week About the role RevCore Pro is building a field-service and operations platform for managing customers jobs scheduling communications payments technicians and mobile workflows. Our immediate priority is making our web and mobile applications feel like mature trusted enterprise products. We want the clarity consistency and operational polish found in products such as Jobber and CompanyCam - not generic dashboards or interfaces that feel assembled from templates or unreviewed AI-generated components. We are looking for a senior product engineer who combines strong frontend craftsmanship with full-stack technical ability. You should care about typography spacing interaction states and workflow clarity as much as database correctness authorization and production reliability. This is a hands-on engineering role. You will personally investigate design implement test and release production features across our Next.js web application backend services and React Native mobile application. This is not primarily a management coordination or ticket-distribution position. Engagement and compensation Fully remote within Poland B2B contractor arrangement 160–300 PLN per hour plus VAT where applicable Initially approximately 20–25 hours per week Opportunity to increase to 40 hours per week based on delivery availability and mutual fit Flexible schedule with dependable overlap for team communication Long-term opportunity for the right person The rate within the advertised range will reflect demonstrated technical level relevant production experience communication and expected ownership. As a general guide 160–200 PLN/hour capable engineer who may require some architectural guidance 200–250 PLN/hour independent senior product engineer 250–300 PLN/hour exceptional senior or lead-level engineer with deep experience across the required stack Initial work distribution The work will initially be approximately 45% web product UI and frontend engineering 25% React Native mobile product experience 20% backend database and integrations 10% testing infrastructure and reliability improvements Testing and edge-case handling are expected throughout all areas. Testing is not something performed only after a feature appears finished. What you will work on You will help develop improve and stabilize an existing SaaS product across web backend and mobile including Customer job and technician-management workflows Scheduling and field-service operations Multi-tenant architecture and permissions Payments and other high-risk integrations Customer and technician communications Offline-capable mobile workflows Push notifications and deep links Reporting dashboards and internal tools Production monitoring and debugging Mobile application preparation and store releases Design-system and component-library improvements Automated regression and edge-case testing Product and interface quality You will help establish and enforce a mature product experience across web and mobile by Creating a consistent design system for typography spacing color components and interaction states Replacing inconsistent generic or unfinished interface patterns Building information-dense enterprise workflows without making them confusing Improving navigation hierarchy forms tables filters scheduling and status visibility Ensuring web and mobile features feel like parts of the same product Designing complete loading empty success error disabled and permission-denied states Building responsive interfaces that work across relevant screen sizes Following appropriate native-mobile interaction patterns Meeting practical accessibility standards Reviewing AI-assisted output critically instead of accepting generated UI or code without understanding it Identifying confusing workflows and proposing better solutions rather than implementing requirements mechanically You do not need to be a dedicated visual designer but you must demonstrate strong product judgment and the ability to translate product requirements into polished production interfaces. Quality and edge-case testing Every feature must account for realistic failure conditions - not only the happy path. You will be expected to Identify edge cases before implementation Create test matrices for permissions roles tenant boundaries and workflow states Write meaningful unit integration and end-to-end tests Test loading empty partial-data and error states Test duplicate submissions retries race conditions and interrupted requests Test timezone scheduling and date-boundary behavior Test offline mobile behavior failed synchronization and conflict resolution Test expired sessions revoked permissions and unauthorized access Test payment failures webhook retries and idempotency Test tenant isolation using explicit negative cases Add regression tests when correcting production bugs Use logs monitoring and reproducible evidence to verify fixes Improve web and mobile test coverage Prevent fragile changes from reaching production through automated CI checks Experience with Playwright is strongly preferred. Experience with Maestro Detox Storybook visual-regression testing or equivalent tools is valuable. Core technology Our stack includes TypeScript React Next.js App Router PostgreSQL Supabase React Native and Expo Expo Router and EAS Stripe Playwright Sentry and production observability Third-party communications and telephony integrations You do not need previous experience with every service listed but you must have strong production experience across the primary web database and mobile technologies. Responsibilities Build complete production features across frontend backend and database layers Work effectively in an existing non-trivial codebase Improve the product without unnecessary rewrites Design secure PostgreSQL schemas queries migrations and indexes Implement and test authorization tenant isolation and row-level security Build production features using Next.js App Router and TypeScript Develop and maintain React Native and Expo functionality Manage mobile build configuration signing and store submissions Integrate payment communications and other external services Write unit integration end-to-end and regression tests Investigate production incidents using logs traces and reproducible evidence Review existing architecture and identify pragmatic improvements Document important decisions and communicate progress clearly Take responsibility for delivered work after it reaches production Raise security usability and reliability concerns before they become production problems Required experience You should have At least five years of professional software-development experience At least three years of substantial React and TypeScript experience Strong recent experience with Next.js including the App Router Strong React CSS and responsive-layout fundamentals Strong PostgreSQL knowledge beyond basic CRUD operations Experience designing authentication authorization and multi-tenant systems Experience with row-level security or equivalent database-enforced isolation Production React Native or Expo experience Personal experience releasing an application through the Apple App Store or Google Play Store Experience building complex SaaS or enterprise workflows Experience creating or extending a reusable design system Experience writing tests for permissions failures and edge cases Experience debugging difficult production problems Experience working in a mature codebase containing established conventions and technical debt Strong written English and the ability to explain technical decisions clearly The ability to work independently and provide concise progress updates You should also be able to demonstrate polished production interfaces—not only landing pages prototypes or template dashboards. Particularly valuable experience We are especially interested in candidates who have worked with Supabase Auth PostgreSQL Storage Realtime or Edge Functions Expo Router EAS Build and EAS Submit Offline-first synchronization and conflict handling Native React Native integrations Background tasks location services and push notifications Stripe or Stripe Connect Playwright or another end-to-end testing framework Maestro Detox or equivalent mobile-testing tools Storybook or visual-regression testing Sentry structured logging and production observability Telephony messaging or communications APIs Field-service CRM scheduling or operations software Large TypeScript monorepos Accessibility testing and responsive enterprise interfaces What strong performance looks like A successful engineer in this role Understands existing systems before changing them Can independently take a feature from investigation through production Produces interfaces that feel deliberate consistent and trustworthy Protects tenant and customer data at multiple layers Tests failure paths permissions and edge cases—not only successful interactions Diagnoses problems using evidence rather than guessing Communicates blockers early and provides concise written updates Uses AI development tools productively while personally understanding and validating the resulting work Improves generated or inherited code instead of accepting it uncritically Makes pragmatic improvements without overengineering Takes ownership of product quality instead of implementing tickets literally Application instructions Please provide one production web or mobile application that best demonstrates your personal product-engineering work. Clearly explain What you personally designed and implemented Which parts were completed by other team members The most complex workflow you owned Your experience with Next.js PostgreSQL and React Native Whether you personally handled mobile signing and store submissions Your requested hourly B2B rate Your weekly availability Shortlisted candidates may be asked to provide a brief Loom walkthrough of existing work. This is not a coding assignment. Credentials customer information and proprietary code may be blurred. The walkthrough may include A complex workflow you personally designed or substantially improved. The underlying components and design-system decisions. Its loading empty error and permission states. A meaningful repository commit or pull request demonstrating your contribution. A PostgreSQL schema RLS policy or tenant-isolation implementation. An automated test covering an authorization or tenant-isolation failure. A React Native or Expo build and release configuration. A difficult production incident and how you diagnosed and verified the fix. Please apply directly. We are currently looking for an individual engineer rather than an agency or outsourced development team. Job Type Part-time Pay 160.00zł - 300.00zł per hour Work Location Remote