According to Elmer of JPButton, the Japanese notice about WebMoney states that you pay the fee for April and they will refund it later back to your WebMoney card.
They don't post the notices for the other languages, since the payment option is Japan-only. I'm amazed there's an English WebMoney error at all when logging in on the American client.
They offer account conversion between NA and EU? I've never heard of that. I wonder why it can't be done to JP accounts. It's not like people don't move to or from Japan any differently than to or from the Americas or Europe...
