Cannot change volume with a2dp_sink_demo

[0x4be473]

Hello,
I am trying to use the included a2dp sink demo with a pico w and a pico audio board and unfortunately I cannot change the volume.
The codes compiles and music does play through the DAC, when reducing the volume to zero the music stops as expected but no in-between, either full volume or mute is possible. (Tried with multiples Bluetooth sources)
Did anyone encounter this problem already or is there a workaround? Thanks!