I'm also having the "Payment System Unavailable" problem. It's a U.S. license and a U.S. credit card. It then tells me
"We're sorry, but we're having trouble processing your order. Please come back and try again later or call us at +1 800-585-0774. If you're not in North America, you can look up a local number here."
I dialed the 800 number and found out that you're only open 5am-7pm PST Mon-Fri. So I tried online help and got to this:
"The best way to contact us...Call an agent Monday-Friday, 5am-7pm PST"
But, it's Saturday here.