Backend Software Engineer

About ZYSYGY 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. 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. Who you are 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've 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've had to ask yourself, "What happens if this fails halfway through?" and actually worked out the answer.Some exposure to financial systems, transactions, or data integrity is a plus — but curiosity and the ability to learn fast matter more than a specific background.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 to people who aren't engineers.Comfortable with ambiguity and early-stage risk. There is no playbook yet. You will help write it.Our stack includes Go, Node.js, Python, React Native, PostgreSQL, and REST APIs over SEPA Instant rails. Experience with any of these is a plus — what matters more is that you pick up new tools fast and care about writing reliable, maintainable code. Strong Bonus (not required) If any of the following apply to you, you will hit the ground running faster than most:You have meaningful hands-on experience building payment systems, fintech infrastructure, or financial APIs.You have designed a ledger and understand double-entry bookkeeping, immutable transaction records, and why you never update a financial row.You have solved the partial failure problem. Money left one wallet and did not arrive in the other. You know how to detect it, resolve it, and prevent it.You understand idempotency at a design level. Your systems survive client retries, duplicate webhooks, and network drops without double-charging anyone.You have built or reasoned about reconciliation: detecting discrepancies between your internal ledger and an external settlement file and resolving them reliably at scale.• You understand KYC and KYB state machines and what a regulator expects from your audit trail. Benefits Be part of a founding team eligible for EXIST Gründerstipendium, a grant from the German government that funds you to build.Flexible hours and fully remote within Germany.Early-stage means something here. Small team, real ownership, no queue of 40 PRs ahead of yours.The problems are genuinely hard. Distributed systems, financial consistency, payment rails, real money moving in real time. If you want to spend your next two years solving problems that actually require you to think, this is the right place.The systems you build will not be thrown away after a demo. They will run in production, handle real transactions, and be used by real people. Your fingerprints stay on it.You will work with people who left stable paths to build a faster, simpler way to move money in Germany. Less bureaucracy, more momentum. If that sounds like your kind of problem, you will fit right in.For the right person who grows with the company, equity is a conversation we will have when the time is right.