Quiz on learningdita.de is not working

[xbln]

I finished lesson 1 with all 3 topics and than started the quiz (German: Test). I got the Test-page
https://www.learningdita.de/tests/test-was-ist-dita/ and hit the start button "Test beginnen", but nothing happened. I tryed different browsers with no success.

I finally registered with the English site and did the same there. Everything worked well. So I am sure that the german website has a problem.