How to get store information in Ebay API with sandbox credentials?

Question

We're implementing integration with Ebay as following:

1. User goes to our site and presses the button.
2. The user is redirected to the authentication page of Ebay, logs in and approves grant of permissions (OAuth).
3. Then we receive the code and exchange it to tokens.

After that with that tokens we need to access store information such as store name, products of the store, orders of the store.

I'm trying to test the calls to GetStore API of Ebay with sandbox user credentials. But I get the Unknown error.

Here is the documentation for the method I call, and it says we need to call SetStore first for sandbox users. But the documentation for the method doesn't exist and the call to the method returns Unknown error: https://developer.ebay.com/devzone/xml/docs/reference/ebay/GetStore.html