I have this problem too and as the previous user says, it works maybe once ever 10 tries. Sometimes the first time of the day, also trying on Switch and then on the webshop on PC sometimes also gives a better chance that it will work. The problem persists even if there is a balance on the paypal account. There seems to be no solution except just keep trying 20, 30 or 40 times a day, every 30 minutes and hope it works before any of the eshop sales are over. This is probably a messed up webservice call or such, maybe a timeout. Error on the Nintento Eshop side: 9001-9310 Error while using Paypal. Error on the Paypal side: Error code 10417 possibly related to security. Also people report that because Nintendo uses a Japanese email adress for their paypal, even if you manage to succeed you may get up to 5-10% fees from your bank if you have it linked because of the foreign transaction fees.
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