If I click fast twice , Why do I end up with -10 coins?

local script:

script.Parent.MouseButton1Click:Connect(function()
    local cost = 10
    local player = game.Players.LocalPlayer
    local leaderstats = player:WaitForChild("leaderstats")
    if leaderstats then
        local coins = leaderstats:WaitForChild("Coins")
        if coins then
                if coins.Value >= cost then
                        game.ReplicatedStorage:WaitForChild("Blue effect coins remove"):FireServer()
                        game.ReplicatedStorage:WaitForChild("Blue effect"):FireServer()
                end
        end
    end

If I click fast then it will become -10 or -20 like that

script:

local BlueEffect = Instance.new("RemoteEvent", game.ReplicatedStorage)
local Blueeffectcoinsremove = Instance.new("RemoteEvent", game.ReplicatedStorage)
BlueEffect.Name = "Blue effect"
Blueeffectcoinsremove.Name = "Blue effect coins remove"
BlueEffect.OnServerEvent:Connect(function(plr)
        local Sparkles = Instance.new("Sparkles", plr.Character.LowerTorso)
        Sparkles.Name = "BlueEffect"
        Sparkles.SparkleColor = Color3.new(0,0,255)
end)

Blueeffectcoinsremove.OnServerEvent:Connect(function(pl)
    pl.leaderstats.Coins.Value = pl.leaderstats.Coins.Value - 10
end)