Add music to your iPhone via Kuaishou and sync it to your phone using iTunes.

However, it is best to synchronize with your own computer, because iTunes will back up the entire iPhone data to the computer.

The smart playlist on the iPhone is like an album. As the number of albums in the database increases, it will move to the back of the list. The red heart is used to count your preferences and provide you with Recommend more similar songs, not for collection. If you want to add it to your favorites, click the menu in the lower right corner and select Add to List.