Senior Full Stack Developer (React, Next.js, Node.js) - OpenAI API Integration for SaaS Web App

We have a web application and want to add AI-powered features using the OpenAI API. We’re looking for an experienced full stack developer who can work inside our existing codebase, solve problems independently, and keep us updated without being chased. What you’ll work on Build and improve features in React and Next.js with TypeScript Develop Node.js / Express services with clean REST API endpoints, documented with OpenAPI Integrate the OpenAI API into our existing app (AI features, prompt handling, error handling, cost control) Manage and optimize our PostgreSQL database (Supabase experience is a plus) Integrate third-party APIs Implement authentication and role-based access Fix bugs and leave clear notes so the next developer isn’t guessing Required React.js / Next.js Node.js / TypeScript / JavaScript PostgreSQL REST API design and integration OpenAI API / AI integration Git / GitHub Nice to have Vercel or AWS deployment Tailwind CSS or Material UI Stripe payments or subscriptions MongoDB / MERN stack experience How we work Fixed-price milestones, starting with one small paid milestone. If it goes well, we continue. A plain-English plan and written scope before coding starts Regular progress updates, and early warning if anything threatens the deadline Readable, maintainable code with handover notes To apply, please include: One project where you integrated an API or AI feature into an existing app, and what the result was Your availability and how soon you can start Your proposed first milestone We’re happy to hire for the long term if the first milestone goes well.