Gentlemen, you are not alone on this issue. I try to purchase Age of Sail awhile back and had the same issue, plus the security trigger event error 1049, don't know if it is from Xsolla or the game site. I used my USAA card and another card, same thing, couldn't buy the game then and have not purchase it yet.
Yesterday, I attempted to purchase this game, first I tried with my USAA card, no luck, same issue. Then I tried my stateside bank (I live in Germany) and was able to get through the process until the amount verification screen. I check my back and there it was, I posted the transaction amount on the webpage, then I got a message that the transaction couldn't be verified at this time and a new window open to contact customer service.
I contacted them, and they reply back very quickly and told me to look at the transaction again and write down a 4 digit code at the end of the transaction and posted on a link they provided, but when I access my account, puff, the transaction was no longer there. They told me to try again today and this time when it comes to the credit card information, they told me to contact their customer service at that point so they can be online in case of issues.
I might try or not, don't know yet. It is very frustrating.