developer product gives more than once credit when purchased?

i have this developer product that allows players to buy 1 skip, but when players buy more than 1 it gives them more than once credit, when it shoud only give them one every time. why?

local buyButton = script.Parent
local productId = 374138275 --change to dev product id
local mps = game:GetService("MarketplaceService")

function getPlayerById(id)
for i,v in pairs(game.Players:GetPlayers()) do
if v.userId == id then
return v
        end
    end
end

buyButton.MouseButton1Click:connect(function()
mps:PromptProductPurchase(game.Players.LocalPlayer, productId)
end)

mps.ProcessReceipt = function(info)
local plr = getPlayerById(info.PlayerId)
if plr and plr:FindFirstChild("NumberOfSkips")  then
plr.NumberOfSkips.Value = plr.NumberOfSkips.Value + 1
print(plr.NumberOfSkips.Value)
    end
end