This is a great point. I'll need to talk to some accountant-types before going forward with this so I can understand what I can and can't book as revenue in thi

This is a great point. I'll need to talk to some accountant-types before going forward with this so I can understand what I can and can't book as revenue in this model. It seems clear that spent credits are revenue, but unused credits live in a kind of gray area, waiting for something to happen. There may have to be an expiry, but I'll make it distant enough that it's unlikely to be hit (i.e. a year). If people look like they're going to hit that expiry period, I'd rather tell them "you're giving us money for something you don't seem to use, maybe it's time to cancel".