Problems with Exam
I bought the exam in the store, but nothing happened.
It's most likely caused by a pop up blocker in your browser. It should work if you tell your browser to make an exception for Duolingo.
The Certificate test failed to start for me more than a week ago (don't give me lingots). I was using the website with Chrome, I got a pop up that gave me the option to cancel but went straight to the "Home page" after clicking "ok" and nothing happened.
After having made an exception to allow pop ups for Duolingo I've been able to take the Certificate test.