Script works fine client side, but not server side?

This script works fine in studio, but not at all in the real game?

This script is a localscript located in the button where you buy the credits

local player = game.Players.LocalPlayer
local player2 = game.Players.LocalPlayer.leaderstats


function CompletePurchase()
    wait(1)
   player.leaderstats.Cash.Value=player.leaderstats.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 = "plr_" .. receiptInfo.PlayerId .. "_pur_" .. receiptInfo.PurchaseId
    ds:IncrementAsync(playerProductKey, 1)  

    return Enum.ProductPurchaseDecision.PurchaseGranted     
end

***I only edited the CompletePurchase function by adding a player argument ***

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

function CompletePurchase(player)
	local stats = player:WaitForChild("leaderstats")
	local cash  = stats:WaitForChild("Cash")
	cash.Value  = cash.Value + 10
end

MarketService.ProcessReceipt = function(receiptInfo) 
    for i, player in ipairs(game.Players:GetChildren()) do
        if player.userId == receiptInfo.PlayerId then
			local ID,PROD = receiptInfo.PlayerID, receiptInfo.PurchaseId 
			
            if receiptInfo.ProductId == productId then
                CompletePurchase(player)
            end
        end
    end 

    local playerProductKey = "plr_" .. ID .. "_pur_" .. PROD
    DataStore:IncrementAsync(playerProductKey, 1) 
 
    return Enum.ProductPurchaseDecision.PurchaseGranted     
end