APEXX Global - Senior Backend Software Engineer

• Own core payment flows end to end: authorisation, capture, refund, void and MIT/recurring across card and APM rails, from design doc to production and beyond. • Own core payment flows end to end: • Evolve our routing and recovery logic: rules-based and data-driven routing, decline cascading, Smart Split and outage failover — making sure a retry never becomes a double charge. • Evolve our routing and recovery logic: • Build and maintain connectors to acquirers, APMs and BNPL providers: normalise responses, handle API version drift and design for partner outages. • Build and maintain connectors to acquirers, APMs and BNPL providers: • Design for correctness under failure: idempotency, timeouts, ambiguous payment states, asynchronous notifications and webhooks, and reconciliation against settlement files. • Design for correctness under failure: • Protect cardholder data: work within our tokenisation and vault services, HSM-backed cryptography and PCI DSS, SOC 2 and ISO 27001 controls, keeping PCI scope as small as possible. • Protect cardholder data: • Run the platform: join the on-call rotation, define and track SLOs and service dashboards, write runbooks, lead incidents and blameless RCAs, and improve our GitLab CI/CD and AWS estate (ECS, Lambda, API Gateway, S3). • Run the platform: • Raise the bar with the team: write technical design docs, give high-quality code reviews, mentor engineers and help us modernise our stack, including our move to Java 17 and newer Spring Boot. • Raise the bar with the team: • Work across the business with Product, Solutions, Support and our UK colleagues, turning merchant and partner needs into reliable systems. • across the business with Product, Solutions, Support and our UK colleagues, • Java and Spring Boot • A strong grasp of distributed-systems failure modes: retries, idempotency, timeouts, concurrency, eventual consistency, and how to reason about "we don't know if it happened". • distributed-systems failure modes: • Solid PostgreSQL skills (schema design, transactions and isolation, query tuning) and practical use of Redis or similar caches. • Redis • Hands-on AWS experience and comfort with CI/CD, containers and infrastructure-as-code. • CI/CD, containers and infrastructure-as-code. • You've owned services in production: on-call, debugging with logs, metrics and traces, leading incidents and writing up what the team learned. • owned services in production: • Clear written communication: design docs, runbooks, RCAs and merge request descriptions that others can act on. • written communication: • You use AI coding tools productively and critically: you know when to trust the output, and you verify it with tests and review before it ships. • AI coding tools • You help the people around you get better through review, pairing and mentoring.