Senior Java Developer – Payment Gateway

About the role

We are seeking a Senior Java Developer to join the engineering team of our US‑based fintech partner. The role focuses on building, maintaining, and enhancing payment gateway solutions that handle card transactions, bank integrations, and payment infrastructure for merchants.

Key responsibilities

• Develop and maintain backend services in Java using Spring Boot, ensuring high reliability and scalability.
• Implement and support payment transaction flows, including ISO 8583 or XML‑based protocols, handling STAN, RRN, reversals, timeouts, and idempotency.
• Work with raw sockets, HTTP transport, TLS, and certificate management to debug intermittent connection issues.
• Collaborate with US and Turkey teams, providing design notes and participating in live calls during overlapping business hours.
• Upgrade and improve inherited codebases, including major framework or dependency migrations.

Required profile

• 6+ years of production backend development in Java with recent Spring Boot experience.
• Hands‑on experience with payment gateways, switches, POS integrations, or direct processor/bank connections, preferably within Turkish payment infrastructure (BKM, VPOS, etc.).
• Strong understanding of card data security, tokenization, 3DES, DUKPT, PIN block handling, and PCI DSS compliance.
• Ability to work independently in a remote, asynchronous environment and provide at least four hours of overlap with US Eastern Time.
• Excellent written and spoken English for documentation and live communication.

Required skills

• Java
• Spring Boot
• ISO 8583 (or equivalent XML protocols such as Fiserv GMF)
• TLS/Certificate handling
• JPA and Spring Data
• SQL
• Payment gateway integration
• Card security standards (tokenization, 3DES, DUKPT, PCI DSS)