I get the message that it couldn't process my credit card - for two different, valid cards in my account, for this book as well as for another (https://vyrso.com/product/42591/passion-how-christs-final-day-changes-your-every-day) :
Worked just now for me.
Working for me. Sorry! [:s]
Seems someone was working on Sunday - or it was just a server hickup: worked again for me now, too.