I thought this was strange too, because previously I had tried (unsuccessfully) to use a mastercard and it did let me select that. This time the pulldown only had the one choice though, visa. Maybe it remembered me and so restricts my account to visa, dunno.
When I had selected mastercard, I was unable to get it to work, probably since my card was a US card. Maybe visa isn't yet blocking these.
UPDATE: the visa payment cleared today

So, at least there's a way to continue using the service