add_items_to_playlist: Add one or more tracks to a user’s playlist.
In tinyspotifyr: Tinyverse R Wrapper for the 'Spotify' Web API

Add one or more tracks to a user’s playlist.

add_items_to_playlist(
  playlist_id,
  uris,
  position = NULL,
  market = "US",
  authorization = get_spotify_authorization_code()
)

`playlist_id`	Required. The Spotify ID for the playlist.
`uris`	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.
`position`	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.
`market`	Optional for music. Required for podcasts episodes. An ISO 3166-1 alpha-2 country code or the string `"from_token"`. Provide this parameter if you want to apply Track Relinking
`authorization`	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’s public playlists requires authorization of the `playlist-modify-public` scope; adding tracks to the current user’s private playlist (including collaborative playlists) requires the `playlist-modify-private` scope. See Using Scopes.