Online Purchase: You can buy Nintendo eShop gift cards directly from the Nintendo eShop or from trusted online retailers like Amazon, Walmart, and Best Buy.
In-Store: Many retail stores sell Nintendo eShop gift cards in physical form, with values like $10, $20, $50, or higher. A value of 3000 could refer to a specific local currency amount, like 3000 yen in Japan, or it may be the equivalent value in other regions.
How to Redeem a Nintendo eShop Gift Card
On the Nintendo Switch:
Go to the Nintendo eShop from the home menu.
Scroll down and select “Enter Code”.
Enter the 16-digit code from your gift card and select “OK”.