Did you added your own Google API key? Look at the help.
Check in YouTube if the id PLItjLOq2rnCREYEUe1De_rt83sjAdy5-2 belongs to a playlist. Check the FAQ of the plugin or send error messages to support.
Error type: "Forbidden". Error message: "Access Not Configured. YouTube Data API has not been used in project 825900879 before or it is disabled. Enable it by visiting https://console.developers.google.com/apis/api/youtube.googleapis.com/overview?project=825900879 then retry. If you enabled this API recently, wait a few minutes for the action to propagate to our systems and retry." Domain: "usageLimits". Reason: "accessNotConfigured".