How to link this to a Citizens NPC:
Instead of having players type /overworldmenu, you can make it so they click a "Miner" NPC to open the shop!

1. Stand where you want the NPC and type: /npc create Miner
2. Make sure the NPC is selected by right-clicking it or typing: /npc select
3. Add the command to the NPC by typing: /npc cmd add overworldmenu