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