"Will you eat?"
Translation:Ти будеш їсти?
Both verb forms (буду їсти/їстиму) of the Ukrainian future progressive are held to be equivalent, and Duo should therefore accept both.
Report if it doesn't.
Mostly here they don't teach the second version because it's harder. As in, I think most of the Duo learners (not actual native speakers) don't know it, so it wasn't accounted for (yet!), but it is 100% correct and should be accepted.