As you know, 3-4 letter domains are hard to come by these days, even with not so popular .tlds. “So”, I had a 3 letter a .so domain to use mainly as an url shortener.
FYI: .so is the tld for Somalia, the source of inspiration for the dankest memes of the internetz.
Apart from the outrageous 99$ renewal fee, what really interesting was; you can NOT renew your domain before it actually expires. So if it expires on 13th march you can not renew it before 14th. It probably does not cause any risk of actually losing the domain of course, whatever the reason, it’s a really strange practice.
As of writing this, you can find more about this and other .SO domain stuff here: https://www.godaddy.com/help/about-so-domain-names-8805 . In all likeliness it will turn into a 404 in a few years, like most of the other links / pages on the internet.