Nintendo has confirmed that credit card transactions at Nintendo eShop & My Nintendo Store will be unavailable due to scheduled maintenance. Read on below for the official announcement from Nintendo of America:
Please note that credit card transactions at Nintendo #eShop & #MyNintendo Store will be unavailable from 5/16 9:00 PM to 5/17 7:00 AM PT due to scheduled maintenance. PayPal will not be affected during this time. We apologize for any inconvenience. http://ninten.do/6010TUSIr
Pokémon Blog 
One thought on “Credit card transactions at Nintendo eShop and My Nintendo Store are now unavailable until May 17 at 7 a.m. PT due to scheduled maintenance”