In English I usually think of "is" being an equal sign with words on either side being interchangeable. Is there a reason DuoLingo rejects writing this in the word order given in the task? "Mwezi wa saba ni kipupwe" is not accepted. 25 October 2019
Please note that you need to report it with the "Report" flag when it marks your answer as wrong. Then the moderators are more likely to see it. Here you are just discussing it with other students, and the discussion so far shows that we already agree with you.