Shopify + Whop Custom Checkout Integration Developer Needed

We are looking for an experienced full-stack ecommerce developer to build a custom checkout integration connecting our Shopify store with our existing Whop account. We do not need a normal Shopify theme customization or a standard Shopify payment-gateway installation. Our intended setup is: Shopify remains our storefront, product catalog, inventory and order-management system. Customers are redirected from the Shopify cart/product page to a custom checkout hosted on our own checkout subdomain. Whop processes one-time and potentially recurring payments. After Whop confirms a successful payment through a verified webhook, the purchase must be created correctly in Shopify as a paid order. Shopify should then handle inventory, fulfillment, tracking and operational order management. Reference implementation: https://checkout.thefaithmade.com/checkout Required scope: Build a secure, mobile-optimized custom checkout. Transfer Shopify cart items, variant IDs, quantities and pricing into the custom checkout. Support customer email, phone and complete shipping-address collection. Integrate Whop Checkout/API for payment processing. Implement and securely verify Whop webhooks. Create corresponding paid orders in Shopify through the Admin GraphQL API. Correctly map Shopify products and variants to Whop products/plans. Synchronize discounts, shipping charges, taxes and order totals. Prevent duplicate Shopify orders if a webhook is delivered more than once. Reduce inventory correctly after successful purchases. Include Whop transaction/payment IDs in Shopify order metadata. Handle failed, cancelled and abandoned payments. Handle refunds and cancellations correctly. Support one-time purchases and subscriptions, if technically supported by Whop. Provide a success/thank-you page and prevent customers from creating unpaid or duplicate orders. Deploy the integration to a production-ready hosting environment. Provide documentation explaining configuration, API keys, webhooks, deployment and maintenance. Security requirements: Raw payment-card information must never pass through or be stored on our server. Whop API keys and Shopify access tokens must remain server-side. Webhook signatures must be verified. The implementation must include idempotency, server-side price validation, logging and error handling. The developer must confirm that the proposed implementation complies with Shopify’s and Whop’s current platform requirements. Please include in your application: Examples of custom Shopify checkout, headless Shopify or external payment integrations you have built. Your experience with Shopify Admin GraphQL API, Whop API and webhook-based integrations. A short explanation of the architecture you recommend. How you will prevent price manipulation and duplicate orders. How refunds, subscriptions and inventory synchronization will work. Your estimated timeline and fixed-price quote. Whether you can provide ongoing maintenance after launch. Please begin your application with the words “WHOP CHECKOUT” so we know you have read the full description. Before development begins, we want a short paid technical-discovery phase confirming: Whop authorizes our business model and products. Our Whop account has the API and checkout capabilities required. The exact Shopify order-creation method. Subscription and refund synchronization. Shopify and Whop platform-compliance considerations. Required skills: Shopify Admin GraphQL API Shopify custom apps Whop API and webhooks Node.js/TypeScript React or Next.js Secure payment integrations Ecommerce checkout development