Don't understand why reward isn't given after purchase?

The script is located in the ServerScriptService, it isn't a local script. I don't understand why this script doesn't work in main game but does in alternative game with different products ids.

local MarketplaceService = game:GetService("MarketplaceService")

MarketplaceService.ProcessReceipt = function(purchaseInfo)
	local plr = game:GetService("Players"):GetPlayerByUserId(purchaseInfo.PlayerId)
	if purchaseInfo.ProductId == 349843507 then
		plr.leaderstats.Coins.Value = plr.leaderstats.Coins.Value + 100
		
	end
	return Enum.ProductPurchaseDecision.PurchaseGranted
end

Well I know a script that can handle that perfectly, in Toolbox search Zed’s Marketplace then click the one that is most Popular with the best logo then in the Purchase Handler put the ProductId in the DevProduct Section like this [ProductId] then under write the amount of coins for example for 200 Coins write 200