It was announced last fall that Nintendo will close the Wii Shop Channel as of January 30th, 2019. With that impending closure the functionality of adding Wii Points as of March.
In preparation for the closure of the Wii Shop, Nintendo will remove the ability to add Wii Points with either a credit card or a Wii Points Card effective March 26, 2018 at 4:00pm ET. If you’d like to purchase Wii Points, you’ll need to do this before functionality is removed.
Once you’ve added Wii Points, you can redeem them for Wii Shop content until the Wii Shop closes.
In the future, Nintendo will be closing all services related to the Wii Shop Channel, including redownloading purchased WiiWare, Virtual Console titles, and Wii Channel, as well as Wii System Transfer Tool, which transfers data from Wii to the Wii U system.
After January 30th, 2019 it will no longer be possible to purchase content from the Wii Shop Channel. Refunds of Wii Points are not possible and it should also be noted that Wii Points cannot be used to fund a Nintendo eShop account or Nintendo Account.
For more information on the closure of the Wii Shop, you can visit https://support.nintendo.com/wii/shopnews.