переделал тип ключа

server/proj/audio/models.py

@@ -22,7 +22,7 @@ class Song(models.Model):
         return f"{self.artist} - {self.title}"
 
 class FavoriteSong(models.Model):
-    song = models.ForeignKey(Song, verbose_name='Трек', on_delete=models.CASCADE, null=True, blank=True)
+    song = models.ManyToManyField(Song, verbose_name='Трек', related_name='song', null=True, blank=True)
     user = models.ForeignKey(MyUser, verbose_name='Пользователь', on_delete=models.CASCADE, blank=True, null=True)
     def __str__(self):
         return f"{self.song.title}"