JMich: Not that I know of. Quick and silly question, but you have entered your CC details, and the button still remains unavailable, right? Because in the screenshot, the button is not available because the details are not filled in.
BrokenToyLol: Of course. I wouldn't show a screenshot with my card details.
gnadenlos: Maybe you are tying to buy an addon without owning the main game?
BrokenToyLol: I have the main game installed.
Wishbone: Have you tried just buying the game through the website rather than through the (officially beta but more accurately alpha) optional client?
BrokenToyLol: Yes.
I've tried buying it through:
-The client
-Internet Explorer (with cache and history cleared)
-Firefox
None of those three options have worked.
I am buying an addon but I have the original game bought on GOG so I shouldnt experience the same issue