I have found a way round this issue. Firstly as you have Google Play Music I presume you also have Google Drive ( free online storage). In this drive create a folder called music, then in this folder create a folder for each artist, say Adele. then in this folder upload mp3 songs of hers you own. You cannot just upload the album it must just be the mp3s.
Then in the Amazon Alexa app go to the skills and enable Personal Jukebox, this will ask you to choose the online storage for Google. Enter user name and password and accept. Job done. Then on Sonos say ‘Alexa Tell Personal Jukebox to play Adele’ (or which ever artist folder you have created). The only issue is that Personal Jukebox shuffles the songs in the folder, but hey at least you can use you cloud storage!