Senior Backend Developer - Node,js (NestJS) Fintech Experience Mandatory

A Senior Backend Developer, you will be responsible for designing, developing, improving,
and maintaining WonnPay's backend platform. You will work closely with the CTO, engineering team, product team, QA, compliance, and external technology partners to build secure, scalable, and reliable backend services. The ideal candidate should be comfortable working independently, making technical decisions,
reviewing other engineers' work, and taking ownership of backend services from design
through production deployment and monitoring

Key Responsibilities:

Backend Architecture & Development

• Design, develop, and maintain scalable backend services using Node.js, NestJS, and TypeScript
• Design robust and maintainable backend architecture for fintech and transaction-based applications
• Develop secure and well-documented RESTful APIs
• Define service boundaries, API contracts, database structures, and integration patterns
• Identify and resolve architectural, performance, and scalability issues
• Refactor legacy or poorly designed backend components when required
• Ensure backend systems are designed for reliability, availability, and maintainability

Database & Data Management

• Design and optimize PostgreSQL databases and relational data models
• Design database schemas, indexes, relationships, migrations, and constraints
• Work with TypeORM or equivalent ORM technologies
• Optimize complex queries and database performance
• Ensure transactional integrity and data consistency
• Design appropriate approaches for handling concurrent transactions and race conditions
• Implement backup, recovery, and data-integrity best practices

Fintech & Transaction Systems

• Develop backend services supporting financial transactions, wallets, payments, and digital assets
• Ensure transaction processing is reliable, traceable, and idempotent
• Handle transaction states, retries, failures, reversals, and reconciliation
• Implement appropriate validation and business rules for financial operations
• Build systems that maintain accurate transaction and wallet balances
• Understand and apply principles of auditability, traceability, and financial data integrity

Third-Party Integrations

• Design and maintain integrations with external APIs and service providers
• Work with payment providers, KYC/AML providers, card issuers, blockchain providers,

and other fintech partners

• Handle API authentication, webhooks, retries, timeouts, rate limits, and failure scenarios
• Build reliable integration layers that can handle third-party service failures
• Monitor and troubleshoot integration issues in production

Security

• Implement secure authentication and authorization mechanisms
• Work with JWT, access tokens, refresh tokens, RBAC, and related security controls
• Protect APIs and sensitive customer data
• Implement secure handling of credentials, secrets, API keys, and environment configurations
• Follow secure coding practices and OWASP principles
• Identify and address backend security vulnerabilities
• Ensure sensitive financial and user information is appropriately protected

AWS & Production Infrastructure

• Work with AWS-based production infrastructure
• Deploy, monitor, troubleshoot, and maintain backend services in production
• Work with services such as ECS, EC2, RDS, CloudWatch, S3, Secrets Manager, Lambda, VPC, or equivalent AWS services
• Support CI/CD pipelines and automated deployments
• Manage environment-specific configurations across development, staging, and production
• Investigate production incidents and perform root-cause analysis
• Improve system observability, logging, monitoring, and alerting

Testing & Quality

• Write and maintain high-quality unit, integration, and API tests
• Ensure critical business and financial workflows have appropriate test coverage
• Participate in code reviews and enforce backend coding standards
• Identify potential production issues before deployment
• Maintain clean, readable, maintainable, and well-documented code

Technical Ownership & Leadership

• Take ownership of backend modules and services from requirements through production
• Review code and provide technical guidance to other backend developers
• Help establish backend development standards and best practices
• Participate in architecture and technical design discussions
• Identify technical risks and communicate them proactively
• Work closely with the CTO and engineering leads on technical decisions
• Mentor junior and mid-level developers when required
• Take ownership of production incidents and drive issues through to resolution

Required Skills & Experience

• 7+ years of professional backend development experience

• Strong background in fintech, payments, banking, crypto, digital wallets, or financial technology platforms, digital wallets,

• Strong hands-on experience with Node.js

• Strong production experience with NestJS

• Advanced knowledge of TypeScript

• Strong understanding of backend architecture and design patterns

• Extensive experience building and maintaining REST APIs

• Strong experience with PostgreSQL or another production-grade relational database

• Strong experience with TypeORM or equivalent ORM

• Experience designing database schemas, migrations, indexes, and optimized queries

• Strong understanding of transactions, concurrency, locking, and data consistency

• Hands-on experience with authentication and authorization systems

• Strong understanding of API security and secure backend development

• Production experience with AWS

• Experience with Git, pull requests, branching strategies, and code reviews

• Experience with automated testing and CI/CD

• Strong debugging and production incident-resolution skills

• Ability to independently analyze problems and make sound technical decisions

Nice to Have

• Experience with Redis and caching strategies
• Experience with message queues such as RabbitMQ, Kafka, or SQS
• Experience with microservices architecture
• Experience with Docker and containerized applications
• Experience with Kubernetes or ECS
• Experience with CI/CD tools and infrastructure automation
• Experience with observability tools and centralized logging
• Experience with blockchain/Web3 integrations
• Experience working with Fireblocks or similar digital-asset infrastructure
• Experience working in a regulated fintech environment
• Experience designing systems for high availability and fault tolerance