Nintendo Points are obsolete. They were the virtual currency for the Wii Shop Channel (closed Jan 2019) and DSi Shop (closed Mar 2017).
You cannot add funds or buy new content. Shops are permanently closed. You can only re-download previously purchased titles (if still on server) via "Settings > Redownload" — but even this may fail as servers degrade.
Buy Nintendo eShop Cards (Target, Best Buy, Amazon, GameStop, Nintendo.com) or link PayPal/Credit Card directly to your Nintendo Account.