Full-Stack Next.js Developer Needed for AI RAG Chatbot & API Integration

We are looking for an experienced full-stack developer to improve an existing SaaS application and add AI-powered features. The application is built with React and Next.js. We need someone who can work across the frontend, backend, database, APIs, authentication, AI integrations, and deployment. Project Scope The selected developer will help us: Review and improve our existing React/Next.js codebase Build backend services using Node.js, NestJS, or Python FastAPI Configure Supabase/PostgreSQL database architecture Implement authentication, role-based access control, and user permissions Develop an AI chatbot using the OpenAI API Build a RAG pipeline using pgvector, Pinecone, or another vector database Integrate LangChain or LangGraph for AI workflows Connect third-party REST APIs and webhooks Integrate Stripe subscriptions and payment processing Connect n8n automation for user onboarding and internal workflows Add proper logging, error handling, testing, and documentation Deploy the application through Vercel or AWS using Docker and GitHub Actions We already have an initial application, so we need someone comfortable understanding an existing codebase, fixing architectural issues, and taking ownership of the implementation. Ideal Candidate You should have strong experience with: React and Next.js Node.js, NestJS, or Python FastAPI TypeScript OpenAI API and AI chatbots RAG and vector databases LangChain or LangGraph Supabase and PostgreSQL REST API and webhook integrations Stripe subscriptions n8n, Make, or Zapier Vercel, AWS, Docker, and GitHub Actions Please share one relevant example where you built or improved a full-stack application containing AI or API integrations.