Senior Backend Developer (Card Payment Systems)

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.

Responsibilities

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

Requirements

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; Hands-on with RESTful API, Webhook integrations; Strong debugging, testing, and system integration skills

Nice to have

Prior banking or fintech experience is highly preferred; Good command of English is a plus; 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