Is "will you make a cake" acceptable
Of course it is
it's a better translation imo
I had "will you make a cake" too and it counted it as wrong
Just report it. As annoying as all of these ''false'' translations are, Korean for DL is still in the Beta so every time you report the correct answer it helps.
When and why are the inquisitive endings like -까 and -니 used? Sometimes they are used for questions like this one, and other times it's a normal sentence with a question mark.