Today I've bought a kindle ebook from amazon.co.jp and when I downloaded it, I've got a warning about my credit card.
I checked my credit card (a prepaid card) and it seems I failed to recharge it the last time, so there weren't enough money to buy the book. Amazon continues to display me the waring about my last order:

"Payment revision needed
Please update your payment method"

But the ebook was delivered right on my kindle even if the payment is not completed.

So now I'm anxious about this issue, because I can not recharge my card untile the next three hours, so I wonder: I'm at risk of ban from amazon japan? :/

I haven't had this particular issue with amazon.co.jp, but I've had it when buying Kindle books from the US Amazon store. I just corrected the payment when I had a chance to do so (in one case it was a couple of days, because I was waiting for a replacement for a lost credit card) and everything was fine.

Thank you Fillanzea! This reassured me xD