I would also pretty much like to have a "invoice" / confirmation email for:
Membership activation / continuation / cancellation (when it does not automatically renews anymore) notice
When Coins are purchased that includes: how much coins are purchased, for how much each coins was purchased (based on membership), and total cost
When Coins are spent, to receive confirmation that a coin was actually spent and to have a general confirmation, this email should include: how many coins are spent (1 in most cases), which title it was, plus a download link (or where to download it, even if it is just https://j-novel.club/user/library)
Also, the current email that is sent out for coins purchased is just not enough, also i dont think a email like admin@j-novel.club should be used, but (like other services do it) noreply@j-novel.club or confirmation@j-novel.club
PS: it would also be nice if these email would be structured like invoice emails to be automatically displayed in something like gmail (like steam does it)