Okay, so I never bought coins in the Korean version, but I tried looking around. I don't know any Korean, so I had to use a translator.
https://gyazo.com/863bc7af7c79af5be50fcc8a612ddf55
The option that I had bubbled in the screenshot says "Overseas Credit Card." If that is selected, then the only credit card options they accept are JCB (Japanese), Discover, American Express, and Diners Club. So if you don't have any of those, then you cannot purchase them from the Korean version. I personally cannot because I only have Visa. Haha.
I bought the physical book in English. The relationship portrayed is really cute and sweet. The two leads have sex with each other's past selves. I thought it seemed awkward at first, but they were really gentle and patient with each other. They also had opportunities to learn more about their partners and had personal growth themselves. It basically made their relationship stronger. Buying the book was worth it.
i wish u could take pics of it and send it to me