I built a production-grade automation web application that lets teams run opt-in WhatsApp campaigns at scale. The platform supports multiple WhatsApp accounts, role-based admin, message templates & media, bulk sending with scheduling, and real-time queue tracking. The system is written end-to-end in TypeScript (Node.js + React) with MongoDB for persistence and a worker/queue layer for high-volume delivery (tested up to ~8,000 recipients per campaign). The design focuses on reliability (idempotency, retries, dead-letter), observability, and policy-compliant usage.