We are looking for a strong backend focused full-stack engineer to take over and stabilize an existing production mobile app. The mobile app is a rewards platform live in the US. The core system is already built. This is not a greenfield build. We need someone comfortable working inside an existing codebase and improving reliability. Primary Responsibilities Initial focus (first 4–8 weeks): • Debug and fix production issues • Strengthen authentication flows (OAuth, email verification) • Improve reward issuance & redemption integrity • Improve logging & observability • Add safeguards • Improve error handling and build strong monitoring system Secondary focus: • Build additional features and maintain detailed documentation • Structure and validate LLM outputs (OpenAI integration) • Implement prompt validation & guardrails • Optimize API usage & cost control Tech Stack Frontend: Flutter Backend: FastAPI (Python 3.11) Database: Cloud SQL Auth: Firebase Hosting: Google Cloud Ideal Candidate • 5+ years backend-heavy full-stack experience • Strong Python + FastAPI experience • Deep understanding of PostgreSQL & transactions • Experience working in existing production systems • Comfortable debugging race conditions & auth issues • Experience implementing idempotent APIs • Experience integrating OpenAI or similar LLM APIs in production • Strong logging & monitoring mindset