Shopify Marketplace Integrations + Stripe Connect

We are looking for an experienced Shopify, WordPress/PHP, and Stripe Connect developer to help build the backend integrations for a multi-brand ecommerce marketplace on our existing website. We already plan to design and develop the logged in brand portal UI/UX ourselves. We need a developer to build the technical connections that allow brands to connect their Shopify stores, sync products, control product publishing, support multi-brand checkout, route orders back to each brand's Shopify store, and handle marketplace payments through Stripe Connect. The goal is to let customers buy products from multiple Shopify-powered brands in a single basket/checkout on our website, while each brand continues managing inventory and fulfillment inside their own Shopify store. Existing Website Stack The existing site is a WordPress/PHP codebase with a custom theme. Relevant stack expectations: - WordPress / PHP - Custom theme integration - Composer-based PHP dependencies - Stripe PHP SDK - jQuery-based frontend behaviour where needed - CSS/SCSS assets - WordPress AJAX, REST API, cron/scheduled jobs, custom database tables, and admin hooks where appropriate We are not looking for a completely separate SaaS app. The work should integrate cleanly with the existing WordPress site. Core Scope We need the developer to build the integration layer for: - Shopify OAuth connection flow for brands. - Secure storage and management of Shopify access tokens. - Product sync from connected Shopify stores. - Syncing products, variants, images, SKUs, prices, inventory, availability, and product status. - Product publishing controls so brands can choose which products appear in the marketplace. - Multi-brand cart/checkout support. - Stripe Connect integration for marketplace payments. - Commission handling, seller transfers, refund handling, and payout logic. - Order splitting by brand after checkout. - Creating the correct order inside each brand's Shopify admin. - Inventory checks before checkout and at order creation. - Shopify webhook handling for product, inventory, fulfillment, cancellation, and refund updates. - Fulfillment/tracking sync back into our website. - Technical hooks/API endpoints that our own brand portal UI can call. What We Are Not Asking For We are not asking this developer to design the brand portal interface from scratch. We will handle the brand portal design and frontend experience. The developer's responsibility is to make the underlying Shopify, Stripe, checkout, sync, order-routing, and publishing-control functionality work reliably. We also do not need a large custom admin dashboard designed from scratch. We mainly need the technical foundations and management hooks so our team can view/manage connected brands, synced products, orders, commissions, payouts, and exceptions. Place holder buttons etc are fine. Important Architecture Requirement This work must be built in a way that can be deployed safely without disrupting the broader website. The ideal implementation should be isolated into a clearly defined module, plugin, or small set of directories/files, so that once tested in staging, we can push only those specific marketplace-related changes live without affecting unrelated areas of the codebase. The developer will work in their own staging environment and should provide clear deployment instructions, file/directory boundaries, database migration steps, environment variables, webhook setup notes, and rollback guidance. Shopify Compliance Requirement Our preferred model is: - Customers browse and checkout on our website. - Customers can buy from multiple connected Shopify stores in one basket. - We collect payment through Stripe Connect. - We keep a marketplace commission. - We pay out the relevant brands. - Orders are created in each brand's Shopify admin for fulfillment. We understand this may involve Shopify sales channel requirements, Shopify app review considerations, and restrictions around external checkout/payment flows. The first stage of the project must include confirming the compliant Shopify architecture and advising what app type, API usage, and approval path is required. Ideal Experience Please only apply if you have strong experience with: - Shopify Admin GraphQL API - Shopify OAuth app development - Shopify webhooks - Shopify product, inventory, and order APIs - Creating Shopify orders from external systems - Stripe Connect marketplace payments - Multi-seller carts and checkout flows - WordPress plugin or custom theme development - PHP/Composer-based integrations - Secure API credential handling - Refunds, cancellations, chargebacks, and payout flows - Ecommerce edge cases and marketplace architecture - Experience building Shopify sales channel apps or external marketplaces connected to Shopify stores is highly preferred.