Senior App & Backend Developer for Custom Offerwall Platform

Project Overview: We are looking for a Senior Full-Stack Developer to build a high-performance, secure "Mega Offerwall Earning App" from scratch. The system must be highly optimized to support 500+ concurrent users with zero lag and solid security. Key Technical Stack: - Backend: Node.js or Go (Golang) - Database & Caching: MongoDB & Redis - Frontend: Native Android Integration Core Requirements & Challenges: 1. Anti-VPN & Anti-Proxy System: Robust detection mechanisms to block fake traffic, device emulators, and unauthorized geo-locations. 2. Offerwall Integration: Integration of 25+ major ad networks and offerwall APIs. 3. Custom Postback Queue Management: A secure, bulletproof postback handler with Redis to prevent double-spending and track accurate user conversions. Project Architecture & Scope: - Project Scale: Large (1 to 3 months duration) - Architecture: Scale-ready, microservices or clean monolithic architecture with properly optimized API endpoints. Payment Term Conditions (Strict): This is a fixed-price contract. Payment will be strictly milestone-based via Upwork Escrow. No advance payments. Milestones will be released ONLY after we receive, comprehensively test, and verify the deliverables to ensure everything works flawlessly under stress conditions. If you have proven experience building complex tracking, ad-network integrated, or high-traffic earning applications, please submit your proposal along with your portfolio/github.