Fix Stripe Subscription Bug in Next.js/Supabase App

We run MedFlow Connect, a small healthcare scheduling platform built with Next.js, Supabase and Stripe. After our latest update, some customers complete Stripe Checkout successfully, but their accounts remain on the free plan. Stripe webhook retries are also creating duplicate subscription records in Supabase. We need someone to identify the cause, fix the billing synchronization, add webhook idempotency, and test upgrades, renewals, cancellations, and failed payments. The GitHub repository, Vercel logs, Stripe test events, and affected account details are ready. This is a small part-time bug-fixing job with an initial budget of $5. However, it may become a long-term contract for a developer who demonstrates strong debugging skills and delivers a reliable solution. Please apply only if you have practical experience with Next.js, Supabase, and webhooks