Fullstack Software Engineer

Tereina

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Location: San Francisco, USA
Job Type: full-time
Work Format: 📍 Onsite
Salary: $150K – $180K
Posted: October 8, 2026

Job Description

About Tereina

Tereina is on a mission to revolutionize B2B payments. We're a well-funded, early-stage startup supported by one of the largest software companies in the world, SAP. We’re building cutting-edge solutions that will transform the way businesses move money. Our platform handles cross-border payment processing, counterparty management, bank account administration, and compliance workflows for enterprise customers worldwide.

Quality engineering at Tereina is about earning confidence in every change we ship — from test strategy and quality tooling through release readiness and the quality evidence our partners and regulators rely on. Our goal is a zero-touch payment process, where payments flow straight through from initiation to the beneficiary without manual intervention. That only works if the software behind it holds up release after release, across every environment.

About the Role

As a Fullstack Software Engineer, you will be pivotal in designing, building, and maintaining web applications and the APIs that power them. You’ll focus on crafting intuitive, secure, and responsive UIs while architecting backend systems that support large-scale financial transactions with real-time processing capabilities.

In an agile environment, you’ll report to the Engineering Manager and work alongside a cross-functional team of engineers, designers, and product managers. This role is ideal for someone who enjoys working across the stack, thrives in early-stage environments, and is passionate about building secure, compliant financial technology.

Key Responsibilities

Frontend Development: Build and maintain modern, responsive, and secure web applications using ReactJS with TypeScript, focusing on performance and accessibility.
UI Frameworks: Leverage React-based libraries to create enterprise-grade UI components that meet financial industry standards.
Backend Development: Design, build, and maintain RESTful APIs and GraphQL endpoints.
Database & Data Management: Design efficient data models and work with SQL and NoSQL databases to securely handle transactional and analytical workloads.
Real-time Systems: Implement websockets, message queues, and event-driven architectures to support real-time payment processing and notifications.
Testing & Quality: Write comprehensive tests using Jest, Cypress, or Playwright to ensure system stability, and participate in code reviews to maintain high code quality standards.
Web Security: In compliance with financial regulations, apply advanced security practices, including CSP implementation, secure coding principles, data encryption, and vulnerability assessment.
Performance Optimization: Implement data compression, caching strategies, CDN optimization, and monitoring to enhance speed, scalability, and system observability.
Collaboration: Work closely with Product, Design, and Platform teams in an agile environment to deliver features that delight customers while meeting compliance and reliability standards.
Mentorship: Participate in code reviews and knowledge sharing, and mentor junior developers as the team grows.

Required Qualifications

Experience: 5+ years of software engineering experience, including significant fullstack development focusing on frontend applications and backend API development.

Technical Expertise:

Strong proficiency in ReactJS and modern JavaScript/TypeScript
Solid experience with backend frameworks (Node.js, Java/Spring, or similar)
Hands-on experience with both SQL and NoSQL databases
Understanding of data modeling and database optimization
Testing: Hands-on experience with Jest, Cypress, Playwright, or other modern testing frameworks, focusing on test-driven development.
System Design: Experience designing scalable web applications, microservices architecture, and API integration patterns.
Agile Development: Experience with Scrum/Agile methodologies, sprint planning, and collaborative development practices.
Problem-Solving: Ability to debug and optimize for performance, security, and reliability.
Communication: Excellent communication skills in a collaborative, fast-paced environment.

Preferred Qualifications

Fintech Experience: Background in fintech, banking APIs, payment processing, or commercial payments systems.
Real-time Systems: Experience with websockets and real-time data processing.
Enterprise UI/UX: Exposure to enterprise-grade UI/UX standards in regulated industries.

Why Join?

Cutting-Edge Work: Build highly scalable applications that power transformative B2B payment solutions using the latest technologies.
End-to-End Impact: Own critical features across the stack, directly influencing product direction and technical architecture.
Security & Scale: Tackle complex engineering challenges in financial compliance, web security, and high-scale distributed systems.
Early-Stage Growth: Shape our technology foundation and engineering culture while growing your career in a well-funded startup.
Learning & Development: Gain deep expertise in fintech, security-first development, distributed systems, and regulatory compliance.
Team Culture: Work with a collaborative, diverse team that values technical excellence, continuous learning, and work-life balance.

We're building transformative technology in payments and looking for curious, driven people to join us. Whether or not you meet every qualification, what matters most is your initiative, willingness to grow, and passion for building secure, performant, and user-friendly web applications.

We embrace AI as a powerful tool for innovation and welcome team members eager to leverage it in their work. As an equal opportunity employer, we’re committed to diversity, inclusion, and creating an environment where everyone can thrive.

🎯 Who is this job for?

Level: Senior Fullstack Software Engineer with 5+ years of experience, ideally including fintech, banking, or payment systems.

Required skills: Strong React, TypeScript, Node.js or Java/Spring, REST and GraphQL APIs, SQL and NoSQL databases, scalable system design, automated testing, web security, performance optimization, and Agile collaboration.

The candidate should be familiar with building responsive enterprise UIs, secure backend services, microservices, real-time systems using websockets or message queues, transactional data models, compliance-focused applications, debugging, code reviews, and mentoring junior engineers.

💬 Potential Interview Questions

How would you design a secure React and TypeScript application for managing cross-border payments?

I would use strongly typed domain models, component-level isolation, accessible UI patterns, and secure state management. Sensitive data would be minimized in the client, protected through secure authentication flows, and validated both client- and server-side.

How would you design a RESTful API or GraphQL service for payment initiation and status tracking?

I would define clear resource and schema boundaries, enforce authentication and authorization, validate all inputs, and use idempotency keys for payment mutations. APIs should expose consistent errors, correlation IDs, audit events, and versioning to support reliable integrations.

How would you ensure payment operations are idempotent and safe to retry?

I would require a unique idempotency key for each client operation and store its result with the request status. Retries would return the original result rather than creating duplicate transactions, while database constraints and transactional updates would provide an additional safeguard.

When would you use SQL versus NoSQL for a financial payments platform?

SQL is appropriate for strongly consistent transactional data such as payments, accounts, and ledger records. NoSQL can be useful for high-volume event data, flexible metadata, or read-optimized workloads, provided that consistency and audit requirements are explicitly addressed.

How would you design an event-driven architecture for real-time payment processing?

I would publish immutable domain events through a durable message broker and use independently scalable consumers for notifications, compliance checks, and analytics. Consumers should be idempotent, support retries and dead-letter queues, and preserve ordering where the payment lifecycle requires it.

How would you implement real-time payment status updates using WebSockets?

The backend would authenticate connections, authorize subscriptions to specific payment or account resources, and publish updates from the event system. Clients should handle reconnects, missed events, duplicate messages, and fallback polling when a WebSocket connection is unavailable.

What testing strategy would you use with Jest, Cypress, or Playwright?

I would use unit tests for domain logic and React components, integration tests for APIs and persistence, and end-to-end tests for critical payment workflows. Tests should cover authorization failures, retries, validation, compliance paths, and failure scenarios rather than only successful flows.

How would you secure a web application handling regulated financial data?

I would apply least-privilege authorization, strong authentication, input validation, encryption in transit and at rest, secure secret management, and comprehensive audit logging. I would also configure CSP and other security headers, protect against common web vulnerabilities, and continuously assess dependencies and runtime behavior.

How would you optimize performance for a React application and its APIs?

On the frontend, I would use code splitting, memoization where justified, efficient rendering, compression, and CDN caching for static assets. On the backend, I would analyze query plans, add appropriate indexes, use caching carefully, paginate large responses, and monitor latency, throughput, and error rates.

How would you design a reliable payment workflow across microservices?

I would model the workflow as explicit state transitions and use an orchestrated or choreographed saga instead of distributed database transactions. Each step would be idempotent, observable, and compensatable where possible, with durable audit records and reconciliation processes for failures or external-provider inconsistencies.

📋 Job Summary

Tereina is a well-funded, SAP-backed fintech startup transforming B2B payments through secure, scalable cross-border payment and compliance solutions. As a Fullstack Software Engineer, you’ll build responsive React and TypeScript interfaces, Node.js or Java/Spring APIs, SQL and NoSQL data systems, and real-time event-driven services, with testing through Jest, Cypress, or Playwright. This is a full-time, hybrid role based in San Francisco or San Diego, offering an estimated base salary of $150K–$180K. Join to shape an early-stage platform, solve high-impact challenges in fintech security and scale, and influence technology that moves money worldwide.