I need a custom Shopify integration that lets customers reserve rental cars directly on my store. The core of the job is wiring my external booking system’s API into Shopify so availability, pricing, and confirmation all flow automatically. Here is the workflow I want to see running smoothly: • A customer chooses dates, sees live vehicle availability, selects extras, and views the real-time price right on the product or dedicated booking page. • When they complete checkout, the integration pushes the booking, customer info, and payment reference to the rental-car system through its REST/JSON endpoints, then returns a confirmation code that appears in the Shopify order and an email to the customer. • If the API reports a conflict or outage, an easy-to-read message prevents the checkout from finishing. I’m not relying on Shopify’s inventory tools for this project—the external booking platform remains the single source of truth, so the focus is entirely on the booking flow, secure authentication, and error handling. You’re free to implement this as a private Shopify app, a custom storefront extension, or another supported approach as long as it meets Shopify’s latest API requirements and keeps page speed fast. Deliverables 1. Source code (Private Shopify app or theme extension) with clear setup instructions. 2. Fully documented API connection, including auth flow, endpoints used, and sample payloads. 3. Embedded date-picker and extras selector styled to match my theme. 4. End-to-end test plan proving successful bookings, failed bookings, and customer notifications. Acceptance criteria • Booking completes in under 5 seconds on a typical 4G connection. • No duplicate bookings when two users select the same car at the same time. • Order ID in Shopify and confirmation ID in the rental system always match for reconciliation. If you have solid experience with Shopify App development, Liquid, and third-party API integrations, this should be right up your alley.