Добавьте файлы проекта.

YandexMusic.API/Models/Search/Track/YSearchTrackModel.cs

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+using YandexMusic.API.Models.Search.Album;
+using YandexMusic.API.Models.Track;
+
+namespace YandexMusic.API.Models.Search.Track
+{
+    public class YSearchTrackModel : YTrack
+    {
+        public new List<YSearchAlbumModel> Albums { get; set; }
+        public bool AvailableAsRbt { get; set; }
+        public bool Explicit { get; set; }
+        public List<string> Regions { get; set; }
+    }
+}

YandexMusic.API/Models/Search/Track/YSearchTrackType.cs

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+namespace YandexMusic.API.Models.Search.Track
+{
+    public enum YSearchTrackType
+    {
+        Music
+    }
+}