I've never actually used it, but from everything I've heard from people I trust, Duolingo is really, really bad for Japanese. I may be biased (I learned Japanese back in the dark ages when "learning apps" weren't a thing), but I'm inclined to think it's better to use nothing at all (i.e. just old-fashioned textbooks, reference books, etc.) than to use a program that is giving you incorrect or misleading answers and explanations.
At the very least, you should be aware than Duolingo is full of problems like this, where minor sentence order changes, using kanji instead of kana (or vice versa), not using the exact phrasing the app expects, etc. etc. can result in a "wrong" answer that's actually perfectly valid.
I suppose you can keep asking here to check when you see something suspicious, and at the very least that will stop you from internalizing misconceptions. I still can't help but feel like Duolingo is more trouble than it's worth, though.