You probably have the same issue as there - please try the steps from there 
If you are comfortable with ssh, could you also let me know if the Volumio API gives us the correct parameters?
You could check by examining the configuration file for vollibrespot
# VLS config
cat data/plugins/music_services/volspotconnect2/volspotify.toml
Also confirm that this matches what Volumio should use
cat /data/configuration/audio_interface/alsa_controller/config.json