ARD viewer

I just downloaded the App to my US Iphone 2. I hope to be able to use it in the US later once I return home from Berlin. However, after downloading, I tried to open the app to test it. As soon as I opened a video link, the screen of my I phone became dark: I cannot run any videos. It must be a bug in the APP, right? Could someone help? Thank you.

Dt. Prof. about tagesschau - Nachrichten