SkipStage script works only with one button but not another?

I have an obby and there is a shop where you can buy a skip 1 stage, skip 3 stages, skip 5 stages or skip 10 stages. When I try to buy the skips, only one works... Here is the local script for the Gui:

 local productId = 1051600749
 local player = game.Players.LocalPlayer
 script.Parent.MouseButton1Click:connect(function()
 	game:GetService("MarketplaceService"):PromptProductPurchase(player, productId)
 end)

Here is the script that I put in "ServerScriptStorage":

local MarketplaceService = game:GetService("MarketplaceService")
local currency = "Stage"
MarketplaceService.ProcessReceipt = function(receiptInfo)
    local player = game:GetService("Players"):GetPlayerByUserId(receiptInfo.PlayerId)
    if not player then
        return Enum.ProductPurchaseDecision.NotProcessedYet 
    end
    if receiptInfo.ProductId == 1051600749 then 
        print("Correct receipt")
        local leaderstats = player:findFirstChild("leaderstats")
        if leaderstats then 
            print("Found leaderstats")
            local currency = leaderstats:findFirstChild(currency)
            if currency then 
                print("Found currency")
                currency.Value = currency.Value + 1
                player:LoadCharacter()
            end
        end
    end
    return Enum.ProductPurchaseDecision.PurchaseGranted 
end

For every scripts, I changed the DeveloperProductId and the Value of the checkpoint to add. When I try to buy the SkipStage that doesn't work, it doesn't print anything that I put in the script... (sorry for the spelling mistakes, English is not my native language)
What's wrong with these scripts ?