I haven't touched this site for years. Any problems with it are because of Youtube changing things in the backgroud. Currently, they are demanding verification, because the site can be authorized to access private playlists. Without verification they automatically block user authorization after 60% of user limit reached. For verification they demand a privacy policy, a terms of service and such things. Since I don't have the time, nor the inclination to deal with this (writing a privacy policy and stuff), the site cannot be authorized after 60% of the daily limit is reached.

I recommend making your playlists public if possible and then you can play them without authorization.