I had the same problem (Australian app store), and today it seems that the situation has returned to normal, but the behavior is slightly different from the previous one.
Now it worked for me:
- Created a new Sandbox user on iTunes Connect.
- Follow the link in the email sent to verify the email address.
- In the application, when interacting with StoreKit, the application will request credentials in the App Store. Enter your username and password.
- The "Verify ID with Apple" warning appears. Click "Settings."
- Change the password according to the instructions.
- In the application, repeat the operation that interacts with StoreKit. This should now work correctly.
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