NPC dropping coins when you click it, help?

I would probably start by making a part inside the NPC model thats about the size of the NPC (A hitbox), turning off CanCollide and making it transparent, then adding a weldconstraint in the model and welding the part to the humanoidrootpart so it sticks to the NPC without it falling out

After that i'd add a clickdetector inside the hitbox part and also a server script.

Add coin model in serverstorage

Inside the coin model add a clickdetector and add a server script inside the coin

Script inside hitbox part:

local coin = game.ServerStorage:WaitForChild("Coin") -- You can change "Coin" to whatever the coin model is called

script.Parent.ClickDetector.MouseClick:Connect(function()
    -- when the NPC's hitbox is clicked:
    print("Clicked")
    -- cloning the coin model and making it spawn by the NPC
    local coinclone = coin:Clone()
    coinclone.Parent = workspace
    coinclone.Anchored = true
    coinclone.Position = Vector3.new(script.Parent.Parent.HumanoidRootPart.X, script.Parent.Parent.HumanoidRootPart.Y, script.Parent.Parent.HumanoidRootPart.Z)
    coinclone.CanCollide = false
end)

Script inside coin code:

script.Parent.ClickDetector.MouseClick:Connect(function(player)
    -- Add whatever you want to happen to the coin when you click it, could add some sounds, particles etc.
    script.Parent:Destroy()
end)

I havent tested this out but it should work, let me know if you get any errors or need more help. Other than that, good luck!