Add one or more tracks to a user<U+2019>s playlist.
add_tracks_to_playlist(
  playlist_id,
  uris,
  position = NULL,
  authorization = get_spotify_authorization_code()
)Required. The Spotify ID for the playlist.
Optional. A character vector of Spotify track URIs to add. For example 
uris = "spotify:track:4iV5W9uYEdYUVa79Axb7Rh", "spotify:track:1301WleyT98MSxVHPZCA6M" 
A maximum of 100 tracks can be added in one request.
Optional. Integer indicating the position to insert the tracks, a zero-based index. For example, to insert the tracks in the first position: position = 0; to insert the tracks in the third position: position = 2 . If omitted, the tracks will be appended to the playlist. Tracks are added in the order they are listed in the query string or request body.
Required. A valid access token from the Spotify Accounts service. See the Web API authorization Guide for more details. Defaults to spotifyr::get_spotify_authorization_code(). The access token must have been issued on behalf of the current user. 
Adding tracks to the current user<U+2019>s public playlists requires authorization of the playlist-modify-public scope; adding tracks to the current user<U+2019>s private playlist (including collaborative playlists) requires the playlist-modify-private scope. See Using Scopes.