use /ah to open the Acution House
Plugin originally made for SpireMC; This is a spigot plugin and I'm using gradle. The plugin works both on spigot and paper servers on 1.21.4, maybe even never versions.
spigot mc page for some images: https://www.spigotmc.org/resources/auction-house.125238/
also modrinth page to download the plugin: https://modrinth.com/plugin/auction-house-plugin