The Seller Portal sandbox is designed to test APIs so not all features of Seller Portal work in the Sandbox (i.e. Reporting).  For security, it is a blank slate and no items are copied from your production account.  You will need to follow the below steps to get data in your sandbox account to test the APIs. But once you’ve set up items, they are there to test all future API updates.

1. Build items using the API, UI or bulk upload templates.
2. Provide inventory quantities to the items using the APIs, UI or bulk upload templates. Set the inventory high enough so you won’t have issues with items running out of stock when generating test orders.
3. Use the Create Purchase Order API to generate test orders on your Sandbox account. This must be done via an API, there is no mechanism in the UI to generate sample POs.
4. You can test the order management, shipment notifications, etc.

For more information, please download the Sears Marketplace API Guide and review the Sandbox Environment section.