Roofstacks

Senior Backend Developer (Card Payment Systems)

Engineering

Employment

Full-time

From the employer

Full Time

Level

Senior

Team

Kart Paketi / RoofMoney

Not doable from Austria

Country assessment

Not doable from Austria because the employer's own board marks it as not remote.

Our assessment is guidance. Confirm arrangements with the employer.

Skills mentioned in this posting

PythonJavaKotlinREST APIs

Job description

At Roofstacks, we’re building innovative financial technologies that power seamless card experiences. We are now looking for a Senior .NET Developer to join our growing Card Payment Systems team. If you're passionate about banking, payments, and high-performance backend development—this opportunity is for you.

🧩 What You’ll Be Doing

You will take part in the full development lifecycle of our card platform, working on mission-critical services used in:

- Card application flows for Debit, Credit, Prepaid, Digital & Commercial cards

- Integrations with KKB/LKS, Decision Support, Analytics Solutions and onboarding systems

- Development of card lifecycle and transaction management services (issuance, renewal, limits, fraud, posting, fee, campaign, extre, DWH etc.)

- Secure integrations with payment schemes (Visa, Mastercard, BKM, CUP, Discover) and EMV scripting/PIN management

- POS ecosystem integrations (TechPOS, Ingenico SDK, CAT transaction flows, parameter distributions)

- Real-time and batch transaction processing with high availability (99.9% uptime) requirements

- Working with ISO 8583 messaging, socket programming, TCP/IP protocols

- Supporting authentication flows via OAuth2, OpenID Connect, JWT/JWS, and 3DS SDK/ACS

✅ What We’re Looking For

- Minimum 5+ years of experience in software development

- Bachelor’s degree in Computer Engineering, Software Engineering, or related field

- Strong experience in C#, .NET Core / .NET Framework

- Solid command of SQL / PL-SQL (Oracle preferred)

- Experience in multi-threaded applications and performance optimization

- Prior banking or fintech experience is highly preferred

- Hands-on with RESTful API, Webhook integrations

- Strong debugging, testing, and system integration skills

- Good command of English is a plus

⚙️ Nice-to-Have Experience

- Experience with other OOP programming languages (such as Java, Python, Kotlin, etc.)

- EMV transaction flow, 3DS 2.x, ACS and GO integration

- Encoding/decoding logic in card-based data formats

- High-performance architecture experience in financial transactions

- Familiarity with scheme compliance (Visa/Mastercard bulletins & updates)

- Experience in distributed system development

- Familiarity with TCP/IP Socket programming, encoding/decoding formats (hex, bcd, ebcdic)

- Understanding of HSM, key management, encryption flows is a plus