There are about 500 black markets(Jangmadang). North Korean regime prohibits its black markets from using foreign currencies in order to control markets under their own will power.
North Korean black markets prefer foreign currencies such as Chinese Yuan and American dollars because of unstable North Korean currencies.
I wonder if North Korea is short of American dollars and Chinese Yuan.
https://imnews.imbc.com/news/2020/world/article/6041701_32640.html