I have subscribed yesterday and this worked fine.
I also wanted to buy 1 more coin - but this did not work: my credit card was declined
I tried it a second time, entered again my payment information... always declined.
After checking my Credit Card transactions, I found, that I had 3 transaction waiting (subscription, 2x buying coins)
Today I got a call from my Card provide who asked if there was a fraud with my card yesterday - it seems that j-novel.club is on a "grey" list: so if there are some strange payments (several small payments nearly at the same time) it get locked.
They told me, that my first transaction went through (subscription), but it was immediately locked after it, so my further transaction have been declined.
I got it now unlocked for 3 month (maximum length) and if I have problems in the future with these payments I should call them again so that they unlock it again.
I am from Austria, so payments to a Japanese website are suspicious :)
Maybe somebody from support can check my payments and contact me (email) when you did not get my payments because: The most important thing is, that I can continue reading my "bookworm" serie :)
The best thing in this situation would be to contact J-Novel Club support directly, as this involves sensitive financial information.
Please explain the situation in your email and someone will be able to look into it.