Senior Full-stack Engineer

<h3>Description</h3> <p><strong>Who are we?</strong></p><p>Papaya Stars is the latest innovation from Papaya, a groundbreaking subsidiary launched to redefine the intersection of social platforms and gaming. Imagine Instagram, Roblox, and TikTok Challenges rolled into one – that’s the revolution we’re building.</p><p>Our mission? Empower creators and players with advanced tools and an immersive platform that’s fun, engaging, and cutting-edge.</p><p><strong>The role:</strong></p><p>We’re looking for a Senior Full-Stack Engineer who thrives in fast-paced, experimental environments. You’ll be the kind of builder who loves turning ideas into end-to-end features - from concept to deployment - combining React Native on the client side with a .NET-based backend.</p><p>This role is backend-oriented but requires strong full-stack ownership, helping us design, develop, and launch monetization-focused and experimental features that drive engagement and growth.</p> <h3>Responsibilities</h3> <ul><li>Design, build, and maintain scalable mobile features using React Native and .NET Core.</li><li>Take features end-to-end - from ideation and prototyping to production rollout and performance optimization.</li><li>Collaborate closely with Product, Design, and Data teams to experiment rapidly, test hypotheses, and improve market fit.</li><li>Implement and iterate on monetization-related functionalities, in-app experiences, and growth-driven mechanics.</li><li>Debug complex technical issues across the stack and improve performance and reliability.</li><li>Contribute to architecture decisions, code reviews, and mentoring as the team grows.</li></ul> <h3>Requirements</h3> <ul><li>4+ years of experience in software development, with hands-on full-stack experience (React or React Native + .NET Core).</li><li>Proven experience building consumer-facing features (B2C, gaming, e-commerce, or social platforms preferred).</li><li>Strong understanding of API design, backend architecture, and cloud environments.</li><li>Practical experience with mobile development (React Native or native mobile).</li><li>Comfort with rapid prototyping, working iteratively, and adapting to changing priorities.</li><li>Ability to handle both feature implementation and DevOps/infrastructure tasks when needed.</li><li>Excellent problem-solving, debugging, and communication skills.</li></ul><p><strong>Nice to have:</strong></p><ul><li>Experience with machine learning algorithms or recommendation systems.</li><li>Experience with GraphQL.</li><li>Familiarity with feature flagging, experimentation frameworks, or A/B testing.</li></ul><p><br/></p><p><strong>What we offer:</strong></p><ul><li>Join a <strong>profitable company with the heart of a startup</strong> – stable, growing, and full of energy.</li><li>Enjoy a <strong>hybrid work model </strong>with flexibility and a growing Warsaw office.</li><li>Receive <strong>competitive compensation tailored to the Polish market - B2B Service agreement</strong></li><li><strong>Comfortable office in central Warsaw equipped with all the necessary tools to conquer the universe</strong></li><li><strong>Luxmed Medical services</strong></li><li><strong>Monthly 'Pyszne.pl' voucher</strong></li><li><strong>Multisport card</strong></li><li><strong>Monthly Happy Hours</strong></li><li><strong>Snacks and Breakfasts</strong></li></ul>