How do I detect a Gamepass that is purchased ingame?

I'm making a game and wanting a GUI to appear when they buy a certain gamepass. I found that MarketplaceService.PromptGamePassPurchaseFinished is a thing, I believe I'm using this incorrectly, how do I properly use this?

	local MarketplaceService = game:GetService("MarketplaceService")
	local DataStore2 = require(script.Parent:WaitForChild("MainModule"))
	local pid1 = 703927122
	local pid2 = 703927252
	local pid3 = 703927369
	local pid4 = 703927502
	local pid5 = 715997494
	
MarketplaceService.ProcessReceipt = function(receiptInfo) 
local newTable = bigCopy(plr)
local MasterData = DataStore2(currentData, plr)
			
	for i, player in ipairs(game.Players:GetChildren()) do
	if player.UserId == receiptInfo.PlayerId then							
		if receiptInfo.ProductId == pid1 then					
			wait(2)
			newTable.Coins = newTable.Coins + 1000
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Visible = true
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Text = "+1,000"
			wait(1)
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Visible = false
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Text = ""
					
		elseif receiptInfo.ProductId == pid2 then
			wait(2)
			newTable.Coins = newTable.Coins + 3000
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Visible = true
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Text = "+3,000"
			wait(1)
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Visible = false
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Text = ""
									
		elseif receiptInfo.ProductId == pid3 then
			wait(2)
			newTable.Coins = newTable.Coins + 7750
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Visible = true
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Text = "+7,750"
			wait(1)
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Visible = false
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Text = ""
							
		elseif receiptInfo.ProductId == pid4 then
			wait(2)
			newTable.Coins = newTable.Coins + 13500
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Visible = true
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Text = "+13,500"
			wait(1)
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Visible = false
			player.PlayerGui.Main.Coins.Coin.AddedAmount.Text = ""
					
		elseif receiptInfo.ProductId == pid5 then				
			wait(2)
			purchaseItem:FireClient(player, "CrateGui")

		elseif MarketplaceService.PromptGamePassPurchaseFinished(7227010) then
			wait(1)
			vip:FireClient(player, "VIPSuccess")
end
end
	MasterData:Set(newTable)
	return Enum.ProductPurchaseDecision.PurchaseGranted	
end
end		
end)

Since, PromptGamePassPurchaseFinished is an event you need to do the following.

local Market = game:GetService("MarketplaceService")

Market.PromptGamePassPurchaseFinished:Connect(function(...) -- Using connect to hook into the event with a function. Also, note the extra args, since this function returns PlayerName, GamePassId, and if the purchase succeeded(Bool, which can return false. Due to cancellations or errors.), in that order. 
	--Code Stuff
	print(...)
end)
--Or Connect With A Prior Function. Usually The Safest Route.
local function Process(...)
	--Code Stuff
	print(...)
end)

Market.PromptGamePassPurchaseFinished(Process)

Try this:

marketPlace = game:GetService("MarketplaceService")

if marketplace:PlayerOwnsAsset(game.Players.LocalPlayer, [YOUR PRODUCT]) then
	-- Something happens
else
	warn("Player does not own the asset")
	-- Probably a script to prompt purchase
end