Based on the information found on the developer's website and the buy page, the only payment method accepted is PayPal. I advise creating an account to link your credit card, because PayPal is very secure and you can file a charge back in case the developer refuses to refund money or it's a scam.
Things complicate when you're using direct payment with credit cards, therefore PayPal assures that you will get your money back in case something bad happens.
