It doesn't work because this is a new course and they are working out the kinks (as my meager understanding of Korean leads me to believe that "closes" should be accepted! ) Hopefully they will make the change soon!
No. 니 is the ending of the question of the 'formal impolite' speech level (also called 'written' or 'diary' speech level)
습니까 is the question ending of 'formal polite' speech level.
Although both serve the same role (creating questions), 니 is NOT a contracted form of 습니까 but an independent grammatical particle and they are used in different contexts