I need to know how to make the player point balance in my game add 100 when a developer product is purchased, this is what I have:

productId = 20619401

local MarketplaceService = Game:GetService("MarketplaceService")
function UsernameFromID(ID)
	if type(ID) ~= "number" then
	return
	end
	local sets = game:service("InsertService"):GetUserSets(ID)
	for k, v in next, sets do
		if v.Name == "My Models" then
			return v.CreatorName
		end
	end
end
function giveRewards(player)
	points = Game:GetService("PointsService")
	player.Character:PromptPurchase(20619401) -- HELP NEEDED HERE
	return Enum.ProductPurcaseDecision.PurchaseGranted
end
MarketplaceService.ProcessReceipt = function(receiptInfo)
	giveRewards(UsernameFromID(receiptInfo.PlayerId))
end
script.Parent.MouseButton1Down:connect(function()
	Game:GetService("MarketplaceService"):PromptProductPurchase(script.Parent.Parent.Parent.Parent, productId)
end)