Rajeev S.

Senior software engineer with 20+ years of experience, specializing in payment systems and AI-powered products. I work hands-on across the stack, from payment architecture and backend services to mobile apps and AI integration. PAYMENTS I design and implement Stripe Connect for marketplaces (Standard, Express and Custom accounts), including payouts, split payments, seller onboarding and KYC. On the subscription side I work with Stripe Billing, Checkout, Elements and PaymentIntents, covering recurring and usage-based billing, proration and failed-payment recovery. Every integration is webhook-driven, with idempotency, retries, refunds, disputes and reconciliation handled properly. I also cover SCA and 3D Secure, decline handling, PCI-DSS-aligned design using tokenization, processor migrations, and in-app purchase flows alongside Stripe. AI CHATBOTS AND AGENTS I build LLM-powered assistants grounded in your own documents and data (RAG), and agents that call your APIs and internal tools to complete tasks. Workflows hand off to a person when confidence is low. Everything integrates with your CRM, helpdesk and billing systems, with logging and evaluation in place after launch. MOBILE, WEB AND BACKEND I have led the design and delivery of 30+ production applications, from first architecture decisions through to launch and long-term support. The work covers iOS, Android and web, including cross-platform apps in Flutter and React Native. Most shipped to the App Store and Google Play, with the surrounding pieces built alongside: backend services, REST APIs, admin dashboards, push notifications, analytics and release pipelines. Because I have seen how these products behave after launch, I design for the problems that appear later, such as scale, failed payments, store review requirements and maintainability. DOMAINS Marketplaces, SaaS and subscription platforms, fintech, health and wellness, rewards and membership apps, ride-hailing and on-demand services. HOW I WORK I scope the work clearly up front, then run it on fixed-price milestones or hourly, depending on the project. You get regular progress updates and a documented handover. For larger builds I work with Subcodevs, a team of senior mobile, backend and UI/UX engineers. Send me a short brief on what you're building and what you need, and I'll reply with an approach and a realistic estimate.