ProcessReceipt wont fire and doesnt work at all?

event.OnServerEvent:Connect(function(player,id,imageid,clothesname)
	
	local mystring = string.lower(clothesname)
	local character = player.Character
	print("test1")
	local function processreceipt(receiptInfo)
		print("test2")
		local playerProductKey = receiptInfo.PlayerId..":"..receiptInfo.ProductId
		local player = Players:GetPlayerByUserId(receiptInfo.PlayerId)
		if not player then
			print('not player')
			return Enum.ProductPurchaseDecision.NotProcessedYet
		end

		if player then
			print('test3')
			if string.find(mystring,"shirt") or string.find(mystring,"suit") or string.find(mystring,"hoodie") or string.find(mystring,"sweater") then
				local shirt = character:WaitForChild("Shirt")
				if shirt then
					shirt.ShirtTemplate = ("http://www.roblox.com/asset/?id="..id)
				end
			elseif string.find(mystring,{"pants","jeans","sweatpants","shorts"}) then
				local pants = character:WaitForChild("Pants")
				if pants then
					pants.PantsTemplate = ("http://www.roblox.com/asset/?id="..id)
				end
			end
			local purchases = player:WaitForChild("leaderstats").Purchases
			purchases.Value = purchases.Value + 1
			print('test4')
			local success,errorMessage = pcall(function()
				PurchaseHistory:SetAsync(playerProductKey)
			end)
			print('test5')
			return Enum.ProductPurchaseDecision.PurchaseGranted
		end	
	end
	MPS.ProcessReceipt = processreceipt
	print('test6')
end)

so this is my script and only print test1 and test 6 fire the processreceipt doesnt fire at all when buying the product(its not a dev product idk if i should be using processreceipt for a 3rd party sale)

How's it supposed to fire if you are not calling it

MPS.ProcessReceipt = processreceipt -- no

In this case you are setting the function itself to the variable so MPS.ProcessReceipt is the function. You need to use brackets and since the function requires 1 argument, pass it into the brackets, so:

MPS.ProcessReceipt = processreceipt(receiptInfo)

receiptInfo should be some other variable but i can't know