you'll need to register one EU NNID and one EU Nintendo Account, and you will probably be able to charge funds with your US card through PayPal (with one of the supported card type)
but... well, no guarantee, as Nintendo officially stated that you need the card issued from your account country.
However, you can also region change the EU 3ds to US (delete eshop profile before doing it if there's already one on it) and see if you can get into eshop, if you can't, ask here again to fix eshop access for region changed console.
#Is it possible to buy things through EU eshop on EU 3ds with American card as payment?
30 messages · Page 1 of 1 (latest)
Certain countries limit payment cards tok ones registered to addresses in their country
You'll need to import points cards to bypass that
Points card must match country of nnid
Game selection and pricing depends on country, you must pick one
You find a store in the target country that will mail you an eshop card or email you the code on it
Like if you set to UK, you can only use UK points cards, or a UK credit card paying in pounds
Can't use a card from Germany
USA can't use Canadian cards, even though same region
Only on a device other than the 3ds
Like what you are using for discord
Needs to be a modern web browser or device
Can do it with pc, phone, switch, etc
Nintendo detailed all of this in their announcement last year
E region accounts have had to do it this way since 2019
The instructions aren't hard to find
Covered it in #announcements
There's not that much terminology
Nintendo has 2 account systems, nnid and Nintendo account
Nnid is old, 3ds and wiiu only, being retired
Nintendo account is the current one, for switch and pc/phone
Nintendo account is all that can add funds as of May or August, globally, and 2019 for Europe /Australia
Nnid can link to Nintendo account to share funds
3ds can't have a Nintendo account
I told you that you link them
Nnid stopped being able to add funds directly in Europe in 2019, rest of world last year
Connect the two accounts, add funds via Nintendo account
You'd need a matching country Nintendo account as nnid to share funds
E region system can only use accounts from the countries in e region
Funds can't share if countries are different