The last few weeks people have been asking Nintendo what was up with the inability to add funds using a credit card. Although they didn't directly respond to any of these, they have now released the latest firmware update, being 10.0.4, which addresses this issue to select countries that were having this issue. Anyone who couldn't pay with a credit card prior should now be able to do so after a quick update to address the problem.

Check out Nintendo's full information on the update here and be sure to update to use credit cards  in the eshop.