Next.js + Stripe developer to take over and maintain live store

Full-stack developer to take over and maintain a live Next.js store I run a small online store for audiobooks and ebooks — customers buy, then stream the audio and read the ebooks in a personal library. There is also a portal where publishers upload their own titles. The site is live and taking payments. It was built by one developer over about six months. He is leaving, and I am not technical, so I need one person who can handle the whole thing: the code and the server. Stack: Next.js 16 (App Router), React 19, TypeScript, Tailwind 4, MongoDB, Redis, NextAuth, Stripe Checkout and webhooks, Cloudflare R2, i18next for four languages. Runs on a VPS with PM2, deployed through GitHub Actions. Three parts, in this order: 1. Take over. Move the repository and all the accounts under my ownership, rotate every credential, set up deploys I can trigger safely with a way to roll back, and add alerts that email me when something breaks. 2. Finish what is pending. There are a few bugs in the checkout flow and a referral feature that is half-built — the database side is done, the screens and API routes are not. There is a full written spec for it, plus architecture documentation, so nothing needs to be reverse-engineered. 3. Ongoing support. Fixes, small features, dependency updates, and being the person I call when something goes wrong. Because I am not a developer, I need someone who explains things in plain language and works in small, reviewable steps. We start with one small paid fixed-price task before committing to anything ongoing. Start your reply with "AUDIOBOOK" and answer these two briefly: - How do you make a Stripe webhook handler idempotent, and what happens if it throws an exception after it has already recorded the event as processed? - Have you deployed and maintained a Next.js app on a plain VPS with PM2, not Vercel? Short and specific is better than a long cover letter.