Senior Java Engineer (Fleet/Payments)

About the Team/Role: We are seeking a seasoned Sr. Java Engineer in the WEX Mobility Engineering organization. This role will sit in the Merchant team within the North America Mobility that caters fleet management and mobility payments solutions to our large customers and partners in the North America region. The Merchant development team spans the USA and Brazil. WEX Merchant products enable discount and rebate programs, secure merchant onboarding, offer management, and transaction and pricing transparency for merchants and partners. At WEX, we deliver reliable, secure, and PCI-compliant services that process high volumes of transactions with strict availability, auditability, and reliability requirements. ​How you’ll make an impact: Design, develop, and maintain robust, scalable, and high-performance object oriented code in our backend services. Develop public REST APIs using Java and internal gRPC APIs for inter-service and inter-system communication. Craft systems designs, lead design decisions, and drive alignment with other senior engineers. Write automated unit tests, integration tests, end-to-end tests, concurrency tests, load/performance tests. Analyze existing systems to identify bottlenecks, tech debt, and implement scalability, and stability improvements. Implement automation for testing, monitoring, healing, and scaling applications, continuous integration and deployment to reduce time to market. Collaborate with cross-functional teams, including product managers, designers, and other engineers, to define and implement new features. Conduct code reviews (comment, approve, seek revisions, merge), mentor junior and mid-level engineers, and actively promote engineering best practices. Dive deep and troubleshoot complex issues, devise fixes, author root cause analysis documents, and ensure lasting performance and reliability. Conduct objective and comparative analyses of competing technologies to advise the team of pros and cons of a technology solution. Maintain robust documentation (design docs, run books, change management docs, and readiness plans). Provide live-site support for production applications by monitoring systems, ensuring rapid incident resolution, and driving continuous improvement. Drive cross-team projects as a single-threaded-owner (STO) or tech lead, and actively unblock other engineers to make progress. ​ Experience you'll bring: Bachelor’s degree in Computer Science or Software Engineering. Senior experience in software engineering. Strong understanding of data structures and algorithms, object-oriented design, and problem-solving skills. Expertise in designing and developing internet-scale services with scalability, availability, security, and reliability design tenets. Excellent written and verbal communication skills, and a collaborative and empathetic mindset. Proficiency in backend development, with proficiency expertise in Java or C#, and frameworks like SpringBoot, building and optimizing RESTful APIs, ODATA framework, and SQL. Ability to leverage AI-enabled development tools such as Cursor AI, Kiro and GitHub Copilot to accelerate feature delivery, automate documentation, and enhance code quality. Fluent English. Preferred Qualifications: Master’s degree in computer science or software engineering. Experience with event-driven architecture and tools like Kafka. Experience working on card payments. Familiarity with cloud-native architecture (containerization using tools such as Docker and Kubernetes). Awareness of API security and PCI DSS compliance requirements. Familiarity with mobile development (iOS or Android). Experience building AI skills & deploying AI solutions to production environments. Experience building production-grade AI agents or copilots. Familiarity with multi-agent systems and distributed AI architectures. Experience with vector databases (e.g., Pinecone, Weaviate, OpenSearch, Milvus). Knowledge of AI evaluation techniques, safety practices, and responsible AI principles.