STAFFXPERT LLC is seeking a Senior MERN Stack Developer (Backend Focus) on behalf of our client in Livingston, NJ to join a growing fintech engineering team. This role is ideal for a highly experienced backend-focused engineer with deep expertise in building scalable APIs, cloud-native applications, and serverless backend systems. The ideal candidate will bring strong experience with Node.js, MongoDB, RESTful API development, and AWS serverless technologies. You will play a key role in designing and maintaining high-performance backend services that support large-scale integrations and mission-critical business operations. Exposure to Python-based development and emerging Generative AI initiatives is highly preferred. Key Responsibilities: Design, develop, and maintain scalable, high-performance RESTful APIs for enterprise-grade integrations. Build secure, reliable, and efficient backend services using Node.js and Python. Develop and support cloud-native applications leveraging AWS serverless architecture, including AWS Lambda and AWS Step Functions for workflow orchestration and service coordination. Contribute to a platform enabling self-service API capabilities for a broad ecosystem of external consumers. Deliver end-to-end backend features independently in a fast-paced, agile environment. Collaborate cross-functionally with engineering teams to drive technical excellence and knowledge sharing. Support platform enhancements and integrations related to Generative AI initiatives. Participate in architecture discussions, code reviews, and backend optimization efforts.