I ran into an issue where all the Verify Apple Id emails I'm getting for Sandbox users are leading to a blank page.
So far I have been unable to verifying a sandbox user due to that.
Tried multiple users and browsers and same issue reproduced with multiple browsers.
Am I missing something or is it just broken?
Login to the created sandbox user on your actual device
As the account is not verified there is a "Verify email" button click on it
Apple will send a code to your email
Enter the code on your device.