At this point, we can only have 1 active store where you may publish listings. If you have multiple accounts then system needs you to specify the active store. Go to Store Settings> 'Select' Your Stores
Here we can see Store 'Optimarch' is marked as active store. Listings will be published only to this eBay account/store. To change store, simply click on the other store from "Your Stores" and select "Market Active". This will make the other store inactive.