Not sure what the status of QoS is right now, but last I checked L7 rules and QoS were not supported. That was about 5-6 years ago and I don’t know if that was ever fixed.
You might want to search these forums and release notes to see if that started working at some point.
Back then I was looking into reserving some bandwidth on the upstream for my Voip phones but realized it was a no go.