I don't know if I got it right but at least is works for me, I can limit or even block spotify connection.
If you have better method or idea you may post it so everyone will know
/ip firewall layer7-protocol
add name=Spotify regexp="^.+(ash.spotify.com).*\\\$"
/ip firewall address-list
add address=78.31.8.0/24 list=spotify
add address=78.31.12.0/24 list=spotify
add address=193.182.8.0/24 list=spotify
add address=194.68.28.0/22 list=spotify
/ip firewall mangle
add action=mark-connection chain=prerouting comment=Spotify disabled=yes dst-port=17808,57621,5736,10000-20000 new-connection-mark=spotify-conn passthrough=yes protocol=tcp
add action=mark-packet chain=prerouting connection-mark=spotify-conn disabled=yes new-packet-mark=spotify-pkt passthrough=no
add action=mark-packet chain=forward disabled=yes new-packet-mark=spotify-pkt passthrough=yes src-address-list=spotify
then create a queue tree or pcq whatever you desire
here's the actual spotify activity using web browser and its application