As all Nintendo Switch players know, you have had to pay 20 euro to play online since the end of 2018. You do that with the online cards with a code on them that you have to enter. When I entered the code this year, everything was normal. Today my IBF (= Internet Best Friend) also wanted to redeem her code, but it didn't work. You received a message that the eShop credit code had already been used. She had never used the card before. What can that be?
The code has already been used, that's why
Probably a nintendo technical problem. Contact support. Has the card expired (in terms of time)? Was she already rubbed free?
The code was already scratched, but not redeemed. It does not know whether the card is still valid
It didn't find an exact date, but it did find a year. It says 2016
