Requests from this Android client application are blocked

Youtube Android API

Requests from this Android client application <empty> are blocked

If you use authorization to create an object 'Youtube'

like:

youTube = new YouTube.Builder(
        transport, jsonFactory, mCredential)
        .setApplicationName(mContext.getString(R.string.app_name))
        .build();

Dont set key in request, like:

YouTube.PlaylistItems.List request = youTube.playlistItems().list("snippet,id");
request.setFields("nextPageToken,pageInfo(totalResults),items(snippet(title,description,thumbnails,publishedAt,resourceId(videoId)))");
//err??? 
//request.setKey(current_key);