This is less of a PSA and more of a "fishbirdthing smacks its face into its fins and laughs until it coughs" thing: whether intentionally or by accident, it seems mojang assassinated the old API involved in whitelisting Minecraft players as a slash command in versions prior to uhhhh 1.20.3 or so. (For those who don't speak Minecraft-ese, that's nearly all the versions. And Minecraft players famously play older versions for a lot of reasons, very frequently.)

How'd I find out? Watching someone try to add a friend to server whitelist so they can fiiiiiinally hop in after making big dewey creacher eyes at them for a mooooooonth.

So the fact that the reddit thread hot tip/answer about why it wasn't working was 14 hours old is giving me feelmotions.