FYI (Pixiv Fanbox)

DLSiteでクレジットカードが使えない問題についての解決策は下記が参考になりそうです。

The following may be a good reference for a solution to the problem of not being able to use credit cards at DLSite.

https://www.reddit.com/r/visualnovels/comments/1fga38y/best_way_to_buy_from_dlsite/