Backend Developer — Multi-Platform Order Hub & Courier Integration (Fulfillment/WMS)

I need a backend developer to build a custom order fulfillment system that pulls orders from multiple e-commerce platforms (Shopify, WooCommerce, Magento, OpenCart) into a single normalized database, checks stock per client, and automatically generates shipping waybills through several regional couriers (Econt, Speedy, Box Now, Pigeon Express, Intime). The stack will be Supabase (Postgres) for the database/API and Appsmith for the admin interface, with custom code handling the platform webhooks, order normalization, and courier API integrations. This is a real business (fulfillment/3PL) going into production, not a prototype — reliability of order intake and waybill generation matters more than polish on the UI.