I need help on implementing a inventory system for my game

hi sorry i got carried away from doing larger objectives rather than focusing on the smaller ones, I will leave this for later as I have an issue where the game says:
image
For context: I am trying to send a message from the enemy.script where should the enemy die it spawns a item onto the players screen like a pickup item when a enemy is defeated.
The code from enemy.script is:

function drop_items(self)
	if self.enemy_health <= 0 then
		local enemy_pos = go.get_position()
		if self.drop_rate > 0.3 then
			msg.post("game:/scroll_spawner", "spawn scroll", {position = enemy_pos})
			print("scroll dropped", enemy_pos)
		else
			print("no scroll dropped")
		end
	end
end
the code for scroll_spawner is
function on_message(self, message_id, message, sender)
	if message_id == hash("spawn scroll") then
		factory.create("#scroll_factory", message.position)
		print("spawned scroll at: ", message.position)
	end	
end

i don’t know how to get rid of the error