I haven’t got time to test it out but it maybe works when you replace steam on line 3 with license.

AddEventHandler('playerConnecting',function(Name,setKickReason,deferrals)	
	for _, v in ipairs(GetPlayerIdentifiers(source)) do
		if string.find(v,"license") then
			setKickReason("Steam has to be open before joining!") -- set reason
			CancelEvent() -- stop player connecting
			break
		end
	end
end)