The global shutdown of the 3DS and Wii U eShops was technically yesterday, but it seems Nintendo has thrown a lifeline out to anyone who still has any codes left to redeem on these digital storefronts.
As highlighted by the company's official Japanese customer support account on Twitter, Nintendo has extended the period to redeem a code after certain technical difficulties with the shops last weekend.
The new end date for code redemption has been updated to 4th April 2023 in Japan. So that's the 3rd April for other regions. During this time you'll be able to redeem game codes, DLC codes, and theme codes via the eShop.
Keep in mind the time frame on game purchases hasn't changed, so it's still only code redemption that's been extended here.