Why is this doubling the value?

I am trying to make a credit shop, and when they buy the dev. product it adds 10 credits to their value When I buy the product it doubles the amount that I already have (ex. I start with 110, and buy it now I have 220... I should only be getting ten)

Heres the script :

local player = game.Players.LocalPlayer
local cash = game.Players.LocalPlayer.Cash

function CompletePurchase()
    wait(1)
   player.Cash.Value = player.Cash.Value + 10
end

local MarketplaceService = game:GetService("MarketplaceService")
local ds = game:GetService("DataStoreService"):GetDataStore("PurchaseHistory")
local productId = 23429504


MarketplaceService.ProcessReceipt = function(receiptInfo) 


    for i, player in ipairs(game.Players:GetChildren()) do
        if player.userId == receiptInfo.PlayerId then


            if receiptInfo.ProductId == productId then

                CompletePurchase()
            end
        end
    end 

    local playerProductKey = "player_" .. receiptInfo.PlayerId .. "_purchase_" .. receiptInfo.PurchaseId
    ds:IncrementAsync(playerProductKey, 1)  

    return Enum.ProductPurchaseDecision.PurchaseGranted     
end

There is also another script :

local buy = script.Parent
local productId = 23429504

buy.MouseButton1Click:connect(function()
    game:GetService("MarketplaceService"):PromptProductPurchase(game.Players.LocalPlayer, productId)
end)

Assuming this is part of a leaderboard do this if not give me the script or scripts associated with that cash value.

player.leaderstats.Cash.Value=player.leaderstats.cash.Value+10

Note that the API states that you must only set "ProcessReceipt" once and you should do it ServerSide. The function is expected to be able to handle any/all purchases, not just of a specific type.

If you make this change and still have issues, add a record of what receipt IDs have been dealt with and if the current receipt ID is in that dictionary, return immediately. ex:

idsDealtWith = {}
MarketplaceService.ProcessReceipt = function(receiptInfo)
	if idsDealtWith[receiptInfo.PurchaseId] then return Enum.ProductPurchaseDecision.PurchaseGranted end
	idsDealtWith[receiptInfo.PurchaseId] = true
	--rest of code here
end

The API actually recommends this code:

local PurchaseHistory = game:GetService("DataStoreService"):GetDataStore("PurchaseHistory")
MarketplaceService.ProcessReceipt = function(receiptInfo)
	local playerProductKey = receiptInfo.PlayerId .. ":" .. receiptInfo.PurchaseId
	if PurchaseHistory:GetAsync(playerProductKey) then
		return Enum.ProductPurchaseDecision.PurchaseGranted --We already granted it.
	end
	--deal with purchase here
	PurchaseHistory:SetAsync(playerProductKey, true)
	return Enum.ProductPurchaseDecision.PurchaseGranted	
end