Why do you fail single Kanji vocabulary words if you put in the kanji reading?

[seanblue]

I like this version from @rfindley:

What do I even call this?

In case it’s not clear yet from the explanations above, here’s an English equivalent: Wanikani: How do you pronounce the letter ‘C’? You: “s” (as in certain) Wanikani: We’re looking for the other pronunciation (“k” as in captain) Wanikani: How do you pronounce the word “CAT”: You: “sat” Wanikani: Sorry, that’s wrong.