Hidden Paid Quest Completed Without My Knowledge

If you don't remember it, it's probably best not to accept it. Considering the gems you'll earn going forward, 60,200 gems is a trivial amount. Quite a while ago, I remember a similar situation where a hidden quest I hadn't completed was marked as completed. When I contacted support, they told me I could just accept it. It seems like contacting support is the best course of action again.

Yeah, I'll try asking them. It'd be lucky if I could get one, but it'll probably be gone before that happens...

This might be solved already, but... Items you can get for free (0 yen purchase) might count towards the conditions.