Unable to listen local files on android

[Viccc_]

I added some local files to my playlist on desktop app and then tried to sync on android mobile.

The song was playing well on desktop but unable to play on my phone(I can see the song in my playlist but it's grey).

I already make sure that they're in same wifi, latest version and switched to download, just can't listen on my phone. 

It's not my first time to add local files on playlist, but naver failed before. 

Maybe anyone can help me solve this? thx so much