Nintendo posted an update to the discontinuation of the the DSi shop service. As of yesterday (9/30/2016) the option to add DSi Points is no longer available. Since you can no longer add DSi points in the DSi shop you’ll have to use any points still remaining in your account, or download any available free games/apps. Nintendo made the announcement earlier this year, with the entire DSi shop discontinuation finalizing on March 31st 2017. Players have until March next year to redeem downloadable games to their DSi systems. The DSi shop channel launched when the system released back in April 5th 2009. The shop service provided over 7 years of quality content, some of which gave the DSi it’s own library of exclusive must play games.
As of September 30, 2016 it is no longer possible to add Nintendo DSi Points to the Nintendo DSi Shop using either a credit card or Nintendo DSi Points Card
There are some DSi (DSiWare) games on the 3DS eShop, up not every DSiware game made it over to the eShop on the 3DS. Make sure to visit the DSi shop before March 31st 2017 to use any points in your account. After that the shop functionality on your DSi will no longer work.