Currently, on 403 the message "Your Watch Later playlist is either full or already contains this video" is shown. This is likely misleading, as the problem is an authorization problem in that case.
If the playlist actually contains the video already,
Currently, on 403 the message "Your Watch Later playlist is either full or already contains this video" is shown. This is likely misleading, as the problem is an authorization problem in that case.
If the playlist actually contains the video already,
is returned. An appropriate message should be shown.