Some songs will not play on Sonos

[LoraMartin]

Hi, 

I have a playlist that plays fully on spotify but ony a few songs will play on my sonos speaker. 

The songs that play on the sonos have a little plus sign next to them that when I hover over says to 'add to Library' there is not this option for the other songs. On the sonos spotify playlist the songs are still there but they are light and can not be clicked on with a little circle with a line going through where the album cover usually is. 

Is it possible that the songs on spotify are comming from my itunes or something like this?

Lastly, when I try and share this playlist only the songs with the plus sign can be played for other spotify users. 

Any advice is welcome, thank you !