In the grammar exercises, it is impossible to distinguish between "sie", as in she and "sie" as in they. Also capital S "Sie" many of the verb tenses are incorrect. I am a fairly novice learner, but I know these errors are in this app. so I wouldnt trust it that much. I found this out after I spent $10 for the passport. I suggest Babbel as an alternative far superior. It costs more, but its worth it.
HariShabad about Learn German - Wie Geht's