Some people who wanted to purchase games on the Switch eShop struggled to complete their orders as the online shop had issues accepting credit cards. Quite a major issue given the fact that a lot of new Switch games came out and...well, plenty of people wanted to purchase them ASAP.
Luckily, Nintendo noted down these issues on their maintenance page and now they have successfully ironed out the problematic bug with a new 10.0.4 update. The update has only one notation - "We have fixed the issue where it was not possible in some countries or regions to add funds using a new credit card or to register credit card information in Nintendo eShop on Nintendo Switch."
It's never pleasant to experience problems like these but Nintendo reacted promptly and we can only thank them for being so quick to iron out the pesky bug. Well done!