Finally, with the ID strings, the list of tracks can be retrieved. Again, the method is described in the web API guide:
https://developer.spotify.com/web-api/get-playlists-tracks/
The method call requires the authorization header:
$tracks = Invoke-RestMethod -Uri https://api.spotify.com/v1/users/$user/playlists/$id/tracks -Headers $headers
The tracks in this particular playlist are shown following:
PS> $tracks.items.track.name The Planets, Op. 32: I. Mars, the Bringer of War The Planets, Op. 32: II. Venus, the Bringer of Peace The Planets, Op. 32: III. Mercury, the Winged Messenger The Planets, Op. 32: IV. Jupiter, the Bringer of Jollity The Planets, Op. 32: V. Saturn, the Bringer of Old Age The Planets, Op. 32: VI. Uranus, the Magician The Planets, Op. 32: VII. Neptune, the Mystic
The web API guide shows other methods that might be used when working with playlists. The application is authorized to use anything that reads information about playlists: