Spotify Desktop - Windows 10.
LG G6 w/ Spotify App.
Both logged into same network.
Windows firewall set to allow Spotify to upload/download.
Songs play fine on desktop, but although the songs are showing up on my phone, they are greyed out. I searched these forums, but none of the solutions worked.
Solution: Windows 10, go to Settings, Network and Internet, Network Sharing Center, Media Streaming (left side). Then click on Media Programs on this PC - Click the Allowed button. This should allow the songs to synch.
Hope this helps!!