Bummer.
I take it it worked before.
Else, you could have run into what I have before ... I run various blockers in my browser. I had to unblock plarium.com. :)
Until I also unblocked x-plarium.com, the store would not work.
I was able to test simply by trying to buy (without the final step of actually doing so). I could not get to the final step until I unblocked. Once I did, I knew I would be good to go at such a crunch time.
Can you try from a browser in safe mode? (i.e. A clean slate - equivalent, create a new profile in chrome or chromium, and do nothing in it. Which removes all extensions in the process. I had to do that tonight to be able to make a payment on a different site. PITA!)
It's probably not them blocking you (they will want your money!), but could be something between you and them. Or rather, their payment site. [Thus the above, where my normal blocks are turned off. (If I forget to unblock both plarium.com and x-plarium.com (could be xplarium.com), payment fails.)]