Senior Java Backend Engineer

Few engineers get to build a national-scale payments system from a blank page. This position puts you at the centre of a greenfield real-time settlement platform: a high-volume, event-driven service that authorises and settles instant payments against prefunded participant balances, and connects directly to national and regional settlement infrastructure.You will join a cross-functional delivery squad as a full member of the team, working from one shared backlog to one shared engineering standard. This is the highest-volume role on the programme, and the work sits squarely on the transactional path, where correctness, resilience and throughput matter most. If you have owned Kafka in production and want your code moving real money in real time, this is the role for you.

Responsibilities

• Design, build and test the prefunded balance engine, covering authorisation, settlement, funding and defunding against participant accounts
• Implement event-driven flows on Kafka with idempotency, exactly-once semantics where required, resilience patterns and full replay capability
• Develop REST APIs governed by OpenAPI contracts for integration with clearing rails and settlement gateways
• Implement payment message handling and build the reconciliation interfaces to downstream settlement systems
• Design transactional data models and tune them for throughput, treating correctness under concurrency as the first constraint
• Run performance and load testing against the defined throughput envelope, then diagnose and remediate the issues found
• Write automated tests as a core part of the definition of done, not as an afterthought
• Contribute to code reviews, technical design discussions and the continuous improvement of engineering standards
• Pair with the in-house engineering team and document work as it lands, keeping knowledge transfer continuous
• Support production readiness through observability, monitoring and clear operational runbooks

Experience and education

Must-Have

• 7+ years of experience building backend services in Java, with strong command of Java 21 and Spring Boot 3.x
• Proven experience owning Kafka in production at high volume, including design, tuning and operational support. Depth here is the primary screening criterion
• Demonstrable experience on systems where correctness under load and failure was critical, such as payments, ledgers, trading or telco billing
• Strong SQL skills and solid understanding of transactional design and concurrency control
• Experience designing and delivering REST APIs using OpenAPI specifications
• Hands-on experience deploying and running services on AWS
• A disciplined approach to automated testing across unit, integration and contract levels
• Bachelor’s degree in Computer Science, Engineering or a related field, or equivalent demonstrable experience

Advantageous

• Payments or financial services domain experience (strongly preferred)
• Knowledge of ISO 20022 payment messaging standards
• Experience with Amazon MSK
• Exposure to Kubernetes and containerised deployments
• Experience with Spring Security
• Familiarity with observability tooling for metrics, logging and tracing
• Performance and load testing experience on high-throughput systems