From Friday 31st March 2017, it will no longer be possible to purchase content in the Nintendo DSi Shop.
Note that even after the Nintendo DSi Shop closes, most DSiWare games will continue to be sold on the Nintendo 3DS eShop.
It is no longer possible to add DSi Points on the DSi Shop.
Make sure to use your remaining Points Cards before then, if you still have any.
Out with the old, in with the new.