Senior Python/FastAPI Engineer — AI-Agent Payments API (x402 / MCP) — Take Over & Extend

I run a live API that serves structured data to autonomous AI agents, monetized via x402 micropayments. Backend is FastAPI/Python on Supabase/Postgres, with an MCP server and multi-chain x402 settlement. The previous contract ended and I'm bringing the work in-house with a new developer. I need someone to take over an existing codebase, verify and stabilize it, and continue the roadmap. This is a take-over-and-extend role, not greenfield. You'll work in someone else's code first — reading it, confirming what works, fixing what doesn't — before building anything new. If that's not your strength, this isn't the role. What you'll do (across staged milestones): Take over the existing repo and deploy it cleanly onto my own hosting (Railway / Netlify / Cloud Run) Verify and stabilize the current x402 / payment feature set Build internal tooling and extend Ongoing feature work against a defined roadmap Must have hands-on, shipped experience: Python / FastAPI Supabase / Postgres x402 payment protocol and/or MCP (Model Context Protocol) servers Multi-chain crypto settlement (EVM + Solana) a strong plus How I work: Written-only communication, fully async (no calls or video) Fixed-price milestones, scope and price agreed before each one starts NDA signed before any repo or infrastructure access I verify every deliverable before release — "done" means it demonstrably works, not "it's pushed" First milestone is small and scoped so we both confirm fit before going further To apply — please answer these. Generic or templated proposals will be ignored: Name one specific x402 or MCP project you've shipped. What did it do, and what was the single hardest technical problem you solved on it? Describe a time you inherited an unfamiliar codebase and got it running in production. How did you approach figuring out what worked and what didn't? You deploy a FastAPI app to a fresh environment. It builds successfully but every request returns a 500. What are your first three debugging steps? First engagement: a small, fixed-price milestone — take over the repo, get the app stable on my infrastructure, and deliver one verified, working result plus a short architecture write-up. Propose your price for that first milestone in your reply. Long-term, milestone-based work if it's a strong fit. This first milestone is the start of a substantial roadmap with ongoing feature development and build-out. I'm looking for someone to grow into the primary developer for the long run, so strong delivery here leads directly to continued milestone-based work.