This answer is requiring the word "some" be included; that has not been required in other cases.
I typed:
"Do you add salt?" (without "some")
and it was marked correct as of Sep 11th 2018.
As of December 30th 2018, it was not marked correct.
''are you adding salt '' should be fine, by me
couldn't you just ask, "ajoutez-vous du sel?"
It should. Next time you come across this exercise translate it that way. But it would be easier and faster to use a translator and double check ;-)
i think I wrote du sel in another case and it was incorrect, "de" was required--pourquoi?