Werkstudent Backend Engineer (m/w/d) - Founding Team

## About the role You will join the core engineering team as a founding engineer. You will own the backend payment engine end to end: transaction flows, wallet management, SEPA Instant settlement, KYB/KYC integration, recurring mandates, refund logic, and the compliance export layer (DATEV, Kassenbuch, GoBD, fiskaltrust). On mobile, you will contribute to the React Native consumer and merchant apps alongside our mobile engineer. You will own what you build from development through deployment, monitoring, and production reliability. The architecture decisions you make in the first six months will run in production for years. ## Responsibilities - Design and build the backend payment engine: transaction flows, wallet management, SEPA Instant settlement, offline payment authorization, and recurring mandate billing. - Own KYB/KYC integration and the compliance export layer: DATEV, Kassenbuch, GoBD, and fiskaltrust for KassenSichV. - Build REST APIs for financial-grade reliability and high-throughput transaction processing, including full R-transaction handling and reconciliation pipelines. - Contribute to the React Native consumer and merchant mobile apps alongside our mobile engineer. - Own the full lifecycle of what you build, from development through deployment, monitoring, and continuous improvement. - Integrate AI tooling into your development workflow as a matter of course: code generation, automated testing, and intelligent review. ## Requirements - Currently enrolled in a Master's or PhD program at a German university, or recently graduated within the last 5 years. - Solid backend engineering foundation. You have built systems that handle real data, you understand databases, APIs, and what happens when things fail. - You think carefully about data consistency and reliability. You have had to ask yourself what happens if this fails halfway through and actually worked out the answer. - You take ownership of what you build end-to-end, from writing the code to making sure it runs in production. - You can explain technical decisions clearly. ## What we offer - EXIST Funding: This role is open to Master's and PhD students or recent graduates (within 5 years) from German universities, eligible for EXIST Gründerstipendium funding. - Remote work within Germany. Open to students at any German university eligible for EXIST Gründerstipendium. - English is the working language of the team. German is a plus but not required. ## About the company ZYSYGY is building Germany's zero-fee payment network. Merchants pay zero transaction fees. We route payments directly over SEPA Instant, bypassing Visa, Mastercard, and the entire card network chain. No hardware. No card reader. Just a phone. We are building the first company to combine a fully software-based merchant POS with a consumer super-app for everyday financial life: payments, transport, utilities, government services, all in one place. Think what UPI did for India. We are doing it for Germany, from the ground up, on banking rails. (website: zysygy.de)