I have this error for all my 500 points challenges since two weeks ago.  I have searched other posts and checked that I am using the same account for my trailhead and my developer.org.  I have tried to use different browsers, Chrome, IE and Firefox to have the same error.  It becomes very frustrated now.  I do have successful experience with the "Check challenge" of 500 points challenge before.

Hi There,
I am trying to complete the module "User Authentication" and in the section "Securing Your Users' Identity" I am trying to complete the excercise, I am having an issue becuase the last task in the excercise involves downloading "Salesforce Authentication" from either iOS store or Google Play store, the issue I am having is that I have a Windows Phone 10 and the app currently is not available in the App Store, can anyone help me with a work around for this please?