Full Stack Web + Backend Developer

═══════════════════════════════════════════════════════════════ JOB POST 1 — FULL-STACK WEB + BACKEND DEVELOPER (the backbone) ═══════════════════════════════════════════════════════════════ TITLE Senior Full-Stack Developer (Next.js + PostgreSQL) — Web App + Backend for a Booking Marketplace DESCRIPTION About the project We're building a booking marketplace for local service businesses (beauty, wellness, fitness) — customers book an appointment in a couple of taps. It will ship as a polished web app AND native iOS/Android apps, all sharing one backend. We have a detailed product specification and a working demo you can reference for every screen and feature. Your role You are the backbone of the build. You own the WEB app and the ENTIRE BACKEND — the database, the booking engine, auth, payments, the API, and deployment. A separate React Native developer will build the mobile app on top of the API you design, so you'll define and document the API contract you both work against. What you'll build - The web application in Next.js (React, TypeScript, Tailwind). - The PostgreSQL data model and a real-time booking & availability engine: slot computation from business hours / staff / buffers, concurrency-safe holds, and a hard guarantee against double-booking (transactions + exclusion constraints), with correct timezone handling. - Authentication and role-based access (customers, vendors, admin). - Card payment integration via our local bank's payment gateway: saved cards, a deposit taken at booking, the customer paying the balance before the appointment, and no-show forfeiting the deposit. - A clean, documented API (REST / tRPC / GraphQL) consumed by both the web and mobile apps, with shared TypeScript types. - Vendor portal (services, staff/resources, calendar/availability, incoming bookings) and admin panel (approve vendors, manage categories/config). - Web + native push notifications; transactional email. - Deployment and DevOps on our own infrastructure (Hetzner): Docker, Postgres with backups and monitoring, SSL, CI/CD. Must-have skills - Next.js (React, SSR) + TypeScript - PostgreSQL: schema design, row-level security, concurrency, performance/indexing - Proven experience building booking/scheduling systems that prevent double-booking under concurrent requests - Payment gateway integration (saved cards, deposits/partial payments, webhooks) - Designing and documenting an API consumed by a separate mobile app - DevOps / self-hosting: Linux, Docker, backups, monitoring, SSL, CI/CD - Tailwind CSS Nice to have - Supabase (self-hosted or managed) - Real-time (WebSockets / logical replication) - Search at scale (Postgres FTS, Typesense, Algolia) and PostGIS / geolocation - Marketplace / multi-vendor experience To apply, please answer (applications that skip these will be ignored): 1. Share a link to a live Next.js + PostgreSQL app you built. 2. Have you built a booking or scheduling system that prevents double-booking under concurrent requests? Briefly, how did you guarantee it? 3. Which payment gateways have you integrated, and did you handle saved cards and deposits / partial payments? 4. Are you comfortable self-hosting on Hetzner (Docker, backups, monitoring) and exposing a documented API for a separate mobile developer to build against? SKILLS (tags) Next.js, React, TypeScript, PostgreSQL, Node.js, REST API, Payment Gateway Integration, DevOps, Docker, Full-Stack Development BUDGET & TIMELINE [Fill in: Fixed-price with milestones, or Hourly $__/hr. This is the lead/backbone role.] Suggested first milestone: database schema + booking engine + a payment proof-of-concept (save card, charge deposit) before the full build.