This is causing a lot of confusion.
I am not a part of Duo Hindi team but I am a native Hindi speaker and I can say with absolute certainty that NO ONE can mark you wrong for using "hai" in a negative sentence. In fact, everyone around me uses "hai" in most of their negative sentences. Dropping "hai" in a negative sentence is quite rare although not incorrect.
Thanks, but this offers no clarity. First, if both variations are correct, that should be made clear to the learner rather than a haphazard appearance of both. I dropped "hai" in two of the exercises and was marked wrong.
Second, the learner should be offered some sense of the actual usage, not just that both are "correct." emrys29 asserts in the previous post that "Dropping "hai" in a negative sentence is quite rare..." I personally don't believe this is true at all. It contradicts authorities like Tej Bhatia and Rupert Snell. (If they are wrong, then by all means they should be corrected, but is the Duolingo team peers of them?) In any case, let us assume it is true. Then learners should be informed that the situation is rare, so they can prioritize doing what is actually most common. Be consistent or explain why it is inconsistent. Is it because previous prominent Hindi grammars are based in Delhi speech, for example? Are both deemed "correct" just because someone has heard someone say each of them? If that's the case, this lesson should be teaching "mere ko," which tons of people say.
You guys really need to do something about this.
Either clearly allow the learner to drop or not drop है and don't mark them wrong for whatever they choose or you mark them wrong consistently for dropping or using it(whatever you decide)