You should probably take note of the “No longer maintained” disclaimer in the title of this post. This means that no development nor updates for this app are taking place. It has been retired.
There is another app, Smouldering Durtles, which is current and being maintained (it is a continuation of the Flaming Durtles app). You may want to look into using that app. [Android] Smouldering Durtles (v1.1.8) - native app with offline lessons and reviews, plus themes and script-like features!