This is my biggest bugbear with the japanese course on duolingo:
Duolingo gives you segments that usually should correspond with full words. Japanese uses a lot of particles that modify a word, indicate its usage in the sentence, or provide further context. These particles are always written in hiragana. Of course you can write any word in hiragana to spell it phonetically, though most often Duolingo teaches you the kanji for specific words.
Two of the most common particles are the topic-marker は and the particle に which is used to mark time or location (similar to the english word “in”). In the above problem Duolingo uses the word 判子 (a personal seal which is used in japan in lieu of signatures) but instead of using the Kanji which it never introduces it uses the hiragana はんこ, and it gives also that combination of hiragana as a whole word segment to select. However, it does not give the に alone but only the combination には despite it not being an actual word, but segments of two words for this sentence combined and the combination of the particles is very much allowed (e.g. here), making this look like two particles when in actuality it wants you to use the は and other hiragana to build はんこ.
This just feels like a bad trap that does not teach anything but only serves as a “gotcha”.