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

Job description

About Zahln Zahln, by 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.: 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. Location Remote within Germany. Open to students at any German university eligible for EXIST Gründerstipendium. Language English is the working language of the team. German is a plus but not required. Tasks **Role Overview **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. What you will do 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. Requir…