So a while ago the banners went up saying "Upgrade your account for only $20!" With a link to the comparison of the account types.
However! To upgrade your account you yourself have to go to a different website, login there with your danbooru account, then upgrade using credit card. No other payment options available.
I truly think it makes no sense to put up the banner advertising upgrading when the process is so strict and convoluted. I am not able to upgrade because I have no creditcard. Creditcards are somewhat rare to own where I am (western europe) so many possibly paying users are missed out here.
If the devs were to smooth out and simplify the process, I'm 100% certain there will be a sizeable increase in updates. Why does this not have more priority? Its been like this with the banner for over a year, possible for a few years.
Make your product easier to consume and more will do so.