"Everyone uses kilometers in our country."
Translation:Ĉiuj uzas kilometrojn en nia lando.
Why not "Ĉiu"? The English sentence has singular too, it doesn't say "all people".
Ĉiu concentrates more one the single person, ĉiuj more on all the persons. In German: jeder/alle. It is difficult to distinguish this in English. It doesn’t say "all people" and it doesn’t say "every single persons." I do not think that the single person here is important.
Ĉiu is correct and should be accepted. It's even a more suitable translation for 'everyone', because it doesn't stress the entireness of the group. I suggest reporting it, until it's accepted. I disagree with jxetkubo that ĉiu somehow concentrates on single persons any more than 'everyone' does.
Duo uses "ĉiuj" in other sentences also, when it doesn't seem to actually make sense. Appears I need to do some research to understand why.