그때 : that time
다르다 : To be different
So it means it is different each time, or shorter, it depends.
It's a pretty common expression, to remember as is.
-Do you like chocolate or vanilla icecream?
-It depends. 그때 그때 달라요.
I feel like "it depends" does not mean the same thing as "it is different every time" at all
It's not english. Different languages use different constructions to provide communication functions.
매번 달라요 should be accepted, unless the context is explicitly disclosed.