Google translates "tu dois du repos" as "you need some rest." But it sounds like Kwiziq only wants us to use devoir before an infinitive. However, the lesson only says "sometimes you can use devoir" without any explanation or examples. Despite the fact that multiple people have been complaining about this for years!
I think also the English translation might be tripping me up in certain instances. Like "you need to take a day off" in English uses the infinitive verb "to take" but in French it's "you need " which is a noun. It would be nice if the lesson explained that.
I hate having to just memorize the quiz maker's answer without understanding why Kwiziq thinks it's correct.