Error type: "Forbidden". Error message: "Requests from referer https://www.googleapis.com/youtube/v3/playlistItems?part=snippet,status&playlistId=&maxResults=8&key=AIzaSyB9efpHvLw3uE8PeeQbiTbdvsPW3ymycIw are blocked." Domain: "global". Reason: "forbidden".

Did you added your own Google API key? Look at the help.

Check in YouTube if the id UC1ZL4QyPL17w-uNOhqC7tzg belongs to a channelid. If the user id is correct, check that the channel of the user has list of "favorites". Check the FAQ of the plugin or send error messages to support.