Part of the core Android and backend team building Simple Invoice Manager (SIM) and Simple Accounting Bookkeeping (SAB) — two live B2B products with 5M+ and 1M+ active users on Google Play Store. Android Development (Java): • Built push-notification-based multi-device sync, enabling real-time data consistency across all user devices • Developed device management module — device listing, last sync tracking — deployed to 1M+ users • Integrated Room DB for offline-first data persistence ensuring seamless UX in low-connectivity scenarios • Used Retrofit + OkHttp for all REST API communication between Android client and Spring Boot backend • Integrated Firebase for push notifications and event tracking • Managed end-to-end Google Play Store releases — versioning, QA, staged rollouts • Delivered Delivery Note feature and multiple client-requested micro-features on tight timelines • Refactored and optimised legacy Java codebase, improving maintainability and reducing technical debt Backend (Java + Spring Boot): • Built and maintained RESTful APIs consumed by Android and web clients serving 5M+ active users • Implemented background task scheduling via cron jobs for automated data processing • Integrated SMTP2GO for transactional email delivery at scale • Monitored and resolved live production issues using Sentry, improving system reliability • Executed full user and data migration from SIM to SAB platform with zero data loss Web Reporting (JSP + AJAX): • Built JSP dashboards with AJAX-powered dynamic filtering, sorting, and reporting • Delivered filtered reports for registrations, deleted accounts, login attempts, and email tracking AI-Powered Productivity: • Use Claude CLI, ChatGPT, and Cursor AI daily for debugging, code reviews, documentation, and workflow automation • Apply prompt engineering techniques to consistently deliver features faster than traditional workflows