Trying to buy from @humblebundle from the UK - it bounces to @stripe for payment and rejects my Visa Debit card. Is it because the Americans only believe in Credit Cards and PayPal? Yes, there is a bit more than £9.50 in my account right now.
There are a number of reasons why your card might've been declined. Your bank will pass the relevant details back to the merchant, so the folks @humblesupport should be able to help you understand what happened here.