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

Zahln is an app that lets you pay with just your phone, no card needed. You scan a QR code or tap your phone, and the money moves instantly. For merchants, it's even simpler, no machine to buy, no contract to sign, just a smartphone, and they keep every euro of the sale instead of losing a cut to Visa or Mastercard.

There are two sides to this. On one side, Studierendenwerke bring us students who use the app every day for things like the Mensa. On the other side, we bring in merchants, so anyone can accept payments just by having a phone. Together that builds a real digital payment system for Germany, a country where over half of all payments are still made in cash.

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 fiscaltrust 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.

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.

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 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 to people who are not 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.

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.

How to apply:

You can apply via our job portal:
https://wellfound.com/l/2CzzTX
or
https://de.indeed.com/viewjob?jk=c28e672409af9849&from=shareddesktop_copy

Connect with the Founder:
Connect with me on LinkedIn: www.linkedin.com/in/shabbir-maimoon