Backend
- Designed and built REST APIs and backend services in Java (Spring Boot, Play Framework) and Scala (Play Framework, Akka), applying OOP principles, SOLID design, and common design patterns (Factory, Strategy, Template Method)
- Handled asynchronous processing — fire-and-forget flows, async event publishing, background task execution — with proper lifecycle and graceful shutdown handling
- Integrated payment gateways end-to-end: designed layered controller → service → webhook architecture, implemented two-phase auth flows, token caching, and callback handling
- Applied aspect-oriented programming for cross-cutting concerns (audit logging, traceability); used event-driven patterns for decoupled async processing
- Maintained clean code through consistent refactoring: service decomposition, parameter object extraction, abstraction of shared behavior, and elimination of duplication
- Wrote unit and integration tests with mocking and embedded database fixtures; ensured test isolation in shared environments
- Designed and executed database migrations; modeled schemas for high-throughput write services; applied polyglot persistence across multiple database technologies
- Built production support tooling for incident recovery; implemented fraud detection at ingestion time with consistent patterns across write services
- Also maintained a PHP/MVC backend: optimized N+1 queries, built parallel query systems, and managed multi-country gateway configurations
Frontend
- Built admin UIs with React / Next.js (TypeScript, Tailwind CSS): typed API client layer, form validation with schema libraries, reusable component patterns wired to real backend APIs
- Designed and built landing pages with clean HTML/CSS/JavaScript across multiple country-service combinations; focused on fast load, responsive layout, and compliance requirements
- Built a modular shared SDK for browser-based authentication flows; applied systematic refactoring to reduce code volume significantly while keeping behavior identical across all regional variants
- Maintained a revenue calculation dashboard: multi-currency tariff logic, per-carrier rate branching, and gateway onboarding integrated into the data pipeline
Communication & Integration
- Authored API contract documentation and integration guides for external partners connecting to our platform — covering webhook flows, subscription protocols, and operator-specific billing rules
- Coordinated directly with gateway providers during onboarding: troubleshot auth handshakes, callback timing, and operator edge cases
- Produced OpenAPI specs as the primary reference for internal and external API consumers