Change volume on sonos group via Alexa

Hi, I've just setup an Alexa-group with my different Sonos speakers, Kitchen, Livingroom and Dining room. I've named the Alexa group "All speakers", and set all the Sonos Speakers as preferred speakers.
This works fine as I can play the Spotify music on all the speakers by saying: "Alexa, play music on all speakers".
But I still cannot change the volume on all the speakers at the same time.
When saying "Alexa, raise the volume on all speakers", it only raises the volume on one of them.
I can raise the volume by telling Alexa to do that room by room. But that is not fast enough.
I always need to pick up my phone and open the Sonos App in order to change the volume on all speakers at the same time, which kind of takes the edge off using Alexa as the controlling device for my Sonos Speakers.
I know that it has been a problem to change the volume on multiple sonos speakers previously through Alexa, but I'm wondering if that is possible now with the new Alexa grouping?
In that case, how is it done?