Following are the API endpoints that helps manage a seamless data transfer between the two systems.

1. Product Catalog API: This enables retailers to manage their product catalog, including creating,  updating, and deleting products, and retrieving product information.
2. Inventory API: This allows retailers to manage their inventory levels, including tracking stock levels, receiving stock, and transferring stock between locations.
3. Order Management API: This enables retailers to manage their orders, including creating, updating, and canceling orders, and retrieving order information.
4. Customer Management API: This allows retailers to manage their customer information, including creating, updating, and deleting customer records, and retrieving customer information.
5. Point of Sale API: This lets retailers process transactions, including creating and updating sales, returns, and exchanges.
6. E-commerce Integration API: This would let retailers integrate their online store with Apparel21, including synchronizing product and inventory information, and managing online orders.