Not working right
When I was learning Esperanto test, I wrote trinkaass for drink. When its supposed to be trinkas and I got it right.
Sometimes Duolingo accepts a slightly different spelling as long as it it close to the real spelling of the word.
And so long as the misspelling couldn't be mistaken for another word (for example, if you typed "weak" instead of "week", it would mark your answer as wrong).