Quite good hint here! This is actually really powerfull, you can even add whole spotify playlists or radio Urls:
#RADIO PARADISE
KEY_1 1 /usr/bin/curl -i --header "Content-Type: application/json" localhost:3000/api/v1/replaceAndPlay --data '{ "service": "webradio", "type": "webradio", "title": "RadioParadise", "uri": "https://stream.radioparadise.com/aac-320", "albumart": "https://radioparadise.com/graphics/logo_flat_350x103.png"}'
#RADIO PARADISE ROCK
KEY_2 1 /usr/bin/curl -i --header "Content-Type: application/json" localhost:3000/api/v1/replaceAndPlay --data '{ "service": "webradio", "type": "webradio", "title": "RadioParadiseRock", "uri": "https://stream.radioparadise.com/rock-320", "albumart": "https://radioparadise.com/graphics/logo_flat_350x103.png"}'
#RADIO EGOFM
KEY_3 1 /usr/bin/curl -i --header "Content-Type: application/json" localhost:3000/api/v1/replaceAndPlay --data '{ "service": "webradio", "type": "webradio", "title": "EgoFM", "uri": "http://mp3ad.egofm.c.nmdn.net/ps-egofm_192/livestream.mp3", "albumart": "https://www.egofm.de/images/site/logo.svg"}'
#GET MORE SPOTIFY PLAYLISTS VIA REST command (install a REST plugin for your browser is recommended): http://volumio.local/api/v1/browse?uri=spotify/playlists
#SPOTIFY RELEASERADAR
KEY_4 1 /usr/bin/curl -i --header "Content-Type: application/json" localhost:3000/api/v1/replaceAndPlay --data '{ "service": "spop", "type": "playlist", "title": "Release Radar", "albumart": "https://newjams-images.scdn.co/v3/release-radar/ab6761610000e5ebda012e44f73353016e419282/en/large", "uri": "spotify:user:spotify:playlist:37i9dQZEVXboZS2Bc5o5qH"}'
#SPOTIFY DISCOVER WEEKLY
KEY_5 1 /usr/bin/curl -i --header "Content-Type: application/json" localhost:3000/api/v1/replaceAndPlay --data '{ "service": "spop", "type": "playlist", "title": "Discover Weekly", "albumart": "https://newjams-images.scdn.co/v3/discover-weekly/aAbca4VNfzWuUCQ_FGiEFA==/bmVuZW5lbmVuZW5lbmVuZQ==/default", "uri": "spotify:user:spotify:playlist:37i9dQZEVXcKMQKnTB7OVv"}'
found this via: