Summary: Seeking a Senior Backend Developer to join an agile team, building scalable systems and contributing to architectural decisions and AI infrastructure from scratch. Highlights: 1. Opportunity to build AI infrastructure from zero 2. High autonomy in technical and product decisions 3. Work on complex integrations across various domains Descripción Our client, a fast\-growing international startup, is redefining how people unlock the value of what they already own, turning circularity into a smart, frictionless payment experience. With a live product, real traction, and a modern tech stack, they are expanding their engineering team with a senior backend profile who enjoys building scalable, resilient systems that have a direct impact on business. If you’re motivated by real technical challenges, modern architecture, and building AI\-driven features from the ground up (not just buzzwords), keep reading. **The Role** The selected candidate will join an agile team with real autonomy. Core responsibilities include: * Designing and building scalable backend systems (Python \+ Django REST Framework). * Working on complex integrations across payments, ecommerce, logistics, and automation. * Participating in architectural decisions and technical roadmap definition. * Driving engineering quality through testing and TDD practices. * Mentoring teammates and contributing to product direction. * Helping build the AI infrastructure from scratch. **What We’re Looking For** **Technical Background** * 5\+ years of backend development experience (senior or lead level). * Strong experience with Python and Django REST Framework (or similar: Ruby on Rails, Phoenix, Laravel, etc.). * Strong testing mindset (ideally TDD). * Knowledge of PostgreSQL, AWS, and security best practices. * Comfortable with occasional frontend work (while remaining backend\-focused). * Solid understanding of system design and scalability. **Product \& Business** * Genuine curiosity about how users experience the product. * Ability to translate design specs into actionable engineering tickets. * Interest in understanding the *why*, not just the *what*. **AI** * Interest in AI for productivity (code generation, automation). * Excitement about building AI features and infrastructure from scratch. * Curiosity about emerging AI capabilities. **Communication** * Fluent in English (spoken and written). Spanish is a plus. * Pragmatic problem\-solver who balances speed and quality. * Collaborative mindset with mentoring experience. **Bonus** * Experience in fintech, payments, or ecommerce. **Tech Stack** * **Backend:** Python, Django REST Framework * **Database:** PostgreSQL * **Frontend:** Angular / Vanilla JS * **Integrations:** PHP (ecommerce plugins) **What the Company Offers** * Competitive compensation. * Fully remote role (optional hub in Barcelona). * Flexibility: 5\-hour overlap with Spanish business hours (9–19 CET). * High autonomy in both technical and product decisions. * Opportunity to build AI infrastructure from zero. * Growing team with strong technical leadership. 60\.000€ \- 80\.000€ Remote 100% Remoto **Persona de contacto:** ediaz@q\-techrec.com \+34 663 444 972