'Det är en jordgubbe, dumbom'
isn't hallon an en world? what are we using the ett form of adjective?
Hallon is an ett word. So the definitive plural is hallonen, which you might have encountered in other sentences (such as we are out of raspberries). Perhaps this got you confused?
I just got a fail thanks to a typo that made 'raspberry' into a 'rasberry'. I felt that was kind of harsh. Is there some sort of logic in what kind of mistakes are accepted? Sometimes one missing/extra/wrong letter is a fail, sometimes it's not.