Could you try again? Fisrt of all it has to be a card in your local country that supports international payment, so it cannot be a debt card or a credit card that only allows local transactions. Additionally, since in my case my Booth was linked to my Pixiv account, my card had to pass on Pixiv first. My first time trying to register my card on Pixiv actually got my account restricted, but after I contacted them to unban me my card also started working.