SpotifyAPI.Web.SpotifyClient.Library.SaveItems error

[eliaskokkalis]

1 public bool AddTracksToLibrary(List<string> trackIds)
2 {
3  if (trackIds == null || trackIds.Count == 0)
4     return true;
5   return spotifyClient.Library.SaveItems(new LibrarySaveItemsRequest(trackIds.Select(x => $"spotify:track:{x}").ToList())).Result;
6 }

This code throws error on line 5:
"Missing required field: uris"
stack trace:
at SpotifyAPI.Web.Http.APIConnector.ProcessErrors(IResponse response)
at SpotifyAPI.Web.Http.APIConnector.d__31.MoveNext()
at SpotifyAPI.Web.Http.APIConnector.d__30`1.MoveNext()
at SpotifyAPI.Web.Http.APIConnector.d__35.MoveNext()
at SpotifyAPI.Web.Http.APIConnector.d__26.MoveNext()
at SpotifyAPI.Web.LibraryClient.d__25.MoveNext()

The error is in SaveItems. Its argument contains Uris