Senior Java Developer

SLEM Technologies; United States; Remote; USD 130,000 - 190,000; Full time

Job summary

SLEM Technologies seeks an experienced Java engineer to lead the design and delivery of payment services. You will own integrations with MPGS and Visa Cybersource and shape secure transaction flows from checkout through settlement, partnering with finance, risk, and operations teams.

You will mentor engineers, improve test coverage, and drive robust API design, idempotency, and fraud controls in distributed systems. Join a fintech-focused team building trusted payment solutions.

Qualifications

• Five+ years building production Java applications, with fintech/payments experience.
• Experience integrating with MPGS and Visa Cybersource.
• Strong Spring Boot, SQL, and API design skills.
• Deep knowledge of card-payment lifecycles, 3-D Secure, tokenisation, settlement, reconciliation, and chargebacks.
• Experience protecting financial data integrity in distributed systems, including idempotency and fault recovery.
• Knowledge of PCI DSS-aware engineering and secure credential handling.
• Comfort with automated testing, Docker, and CI/CD, plus ability to mentor engineers.

Responsibilities

• Design and maintain payment APIs using Java and Spring Boot, including gateway integrations.
• Manage transaction states, idempotency, retries, duplicate prevention, and recovery.
• Build tokenisation, 3-D Secure, authorisation, capture, void, refund flows, and gateway notifications.
• Maintain auditable transaction records and ledger integrations; support settlement reconciliation and exception handling.
• Apply payment security practices and protect credentials; prevent sensitive data from appearing in logs.
• Investigate payment incidents, review performance, improve automated tests, and mentor engineers.

Skills

Java

Spring Boot

API design

Fintech payments

CI/CD

Mentoring

Education

Bachelor's degree in Computer Science or related field

Tools

Docker

SQL

Job description

Role overview

Lead the design and delivery of Java services for payment products, with hands-on ownership of integrations with MPGS and Visa Cybersource. Shape secure transaction flows from checkout and authentication through settlement and reconciliation, while working with finance, risk, and operations teams and helping other engineers make sound technical decisions.

Responsibilities

• Design and maintain payment APIs using Java and Spring Boot, including integrations with both gateways.
• Manage transaction states, idempotency, retries, duplicate prevention, and recovery when a gateway response is unclear.
• Build tokenisation, 3-D Secure, authorisation, capture, void, refund, and gateway-notification flows.
• Maintain auditable transaction records and ledger integrations; support settlement reconciliation and exception handling.
• Apply payment security practices, protect credentials, and prevent sensitive card data from appearing in application logs.
• Investigate payment incidents, review performance, improve automated tests, and mentor engineers.

Requirements

• At least five years building production Java applications, including substantial fintech or payment-processing experience.
• Production integration experience with both MPGS and Visa Cybersource.
• Strong Spring Boot, SQL, and API design skills.
• Deep knowledge of card-payment lifecycles, 3-D Secure, tokenisation, settlement, reconciliation, and chargebacks.
• Experience protecting financial data integrity in concurrent, distributed systems, including idempotency and fault recovery.
• Working knowledge of PCI DSS-aware engineering and secure credential handling.
• Confidence with automated testing, Docker, and CI/CD, plus experience guiding developers and communicating clearly.

Nice to have

• Experience with acquiring banks, payment orchestration, or multi-currency settlement.
• Familiarity with fraud controls, dispute handling, or event-driven financial systems.