Over the past few years, Nintendo has been gradually dropping support for the Nintendo 3DS and Wii U and they focus all of their work and resources on the Nintendo Switch. The process has been slow, but Nintendo has decided that the time has come to end support for yet another thing on the 3DS and Wii U.
Nintendo has announced earlier tonight that “the handling of credit cards and transportation e-money in the Nintendo eShop on the Nintendo 3DS series and Wii U will be terminated at 9:00 a.m. on January 18th, 2022 (Tuesday). After the termination, you will no longer be able to add balances using credit cards and transportation e-money from the Nintendo 3DS series and Wii U”.
The good news is that this change is mainly for direct payments. You can use indirect methods, such as the Nintendo Switch, to be able to add funds to the 3DS and Wii U eShops. But it is yet another sign that Nintendo has, unfortunately but unsurprisingly, decided to move on from the 3DS and Wii U.