I'm trying to make a Buy Bullet system, how do I get it to work?

Server Script:

game.ReplicatedStorage.ChangeBullet.OnServerEvent:Connect(function(plr, bullet)
    if game.ServerStorage.BulletTypes:FindFirstChild(bullet) then
        plr.HiddenStats.BulletType.Value = bullet
    end
end)

Local Script:

local plr = game.Players.LocalPlayer

script.Parent.MouseButton1Click:Connect(function()
    if not plr.HiddenStats.BulletType.Value == "Default" then
        game.ReplicatedStorage.ChangeBullet:FireServer("Default")
    end
end)