I have this strange problem where I can't make any payment transactions on the eShop. If you could help, I'd be forever grateful .

Is your card able to accept online transactions?

Can you buy things online from other stores, or is it just the eShop that is problematic?

What error code are you getting? I read this on another forum:

"I fixed it tried the solution for error code 005-6535

1.Change the Region Setting to Canada 1.From the Nintendo 3DS HOME menu, select "System Settings."
2.Select "Other Settings," then "Profile."
3.Select "Region Settings," then select Canada (this will be changed back to United States in a moment).
4.Select "OK" twice, "Back" twice, then "Close" to return to the Nintendo 3DS HOME menu.

2.Enter the Nintendo eShop 1.Select the Nintendo eShop icon, then select "Next" twice.
2.Select "I agree," "Next," then "Confirm."
Note: You will see a notice about how the change in country settings affects your funds. Your funds will become accessible again once the country is changed back to United States at the end of this process.

3.Select " any province, and select "OK" twice to enter the Nintendo eShop. •If prompted to link to Club Nintendo, select "Skip."

4.Press the HOME Button and select "Close" to exit the Nintendo eShop.

3.Change the Region Setting to United States 1.Select "Other Settings," then "Profile."
2.Select "Region Settings," then select United States.
3.Select the state, then "OK."
4.Select "Back" twice, then "Close" to return to the Nintendo 3DS HOME menu.

4.Update the Zip code in the Nintendo eShop 1.Select the Nintendo eShop icon, then select "Next" twice.
2.Select "I accept," "Next," then "Confirm." •If prompted to link to Club Nintendo, you may choose to do so now, or you may select "Skip" to link your account at a later time.

3.Select the "Menu" button from the top-left of the touch screen.
4.Scroll down and select "Settings / Other."
5.Scroll down and select "Location Settings."
6.Enter the zip code, then select "OK."
7.Verify that your city, state, and county are correct, or select the city, state, and county if prompted.
8.Select "OK" twice to confirm your location settings. "

That fixed it. Thanks a ton ^_^.

hahah i got this same error but i just called the nintendo support person they told me those exact steps

Glad you've got it all figured out, then :3