You need to install resourcepack for java edition first. (Itemsadder, Oraxen, Nexo or default server resource pack)
You also need Vegas plugin and Geyser plugin.

Then:
1) Open your server folder -> plugins folder -> Vegas folder -> config.yml -> set true to the option "Developers GUI resource pack enable: true" if this option exists! After activation this option will disappear from the config.
2) Open your server folder -> plugins folder -> Geyser-Spigot folder
3) Move "geyser_vegas_guis_mappings.json" to custom_mappings folder
4) Move "vegasGUI.mcpack" to packs folder.

Start your server
Write, for example: /casino create Darts