We operate a live mobile marketplace app (not an MVP) and are seeking a senior, hands-on backend engineer to help diagnose and stabilize production issues. This role is not about building new features. It is about fixing what breaks under real user load. Current issues include: Duplicate job creation caused by race conditions Occasional crashes during peak traffic Backend reliability issues in a PHP/MySQL API Tech stack: Mobile app: Flutter Backend: PHP Database: MySQL Infrastructure: AWS (EC2 / RDS) Payments: Stripe Scope (Phase 1 – Paid Audit): Review backend PHP code and API flows Analyze MySQL queries, indexes, transactions, and concurrency Identify root causes of duplicate actions and crashes Review logs and production behavior (read-only access) Deliver a written diagnosis and concrete fix plan Important constraints: This starts as a paid audit only (6–10 hours) No production changes without approval Read-only access initially You must be the person doing the work (no delegation or agencies) We are looking for someone who: Has real experience debugging production systems Understands idempotency, race conditions, and database locking Is comfortable tracing issues across mobile → API → database Can explain why systems fail, not just apply “best practices” We are NOT looking for: MVP builders Feature-only developers Junior engineers Agencies or outsourced teams To apply, please include: A brief description of a production issue you personally diagnosed and fixed How you would approach preventing duplicate actions in a PHP/MySQL API Your hourly rate and availability over the next 1–2 weeks If the audit goes well, there is follow-on stabilization work available.