"Cannot connect to App Store" when trying to purchase subscription using Xcode built app

I'm developing an app and I think I've implemented what I need to in the swift code. However, when I click the Purchase button in my app, I see "Cannot connect to App Store" when the App Store app opens. Attached are images showing how I've configured the Sandbox user. What am I doing wrong? I expect to be able to do a fake purchase to test subscription activation in the app, but it doesn't work.