DBus bluez properties - Volume

[lukasz20]

I am trying to find commands to set and get volume of bluetooth headphones from the terminal. There are VolumeUp and VolumeDown methods available in org.bluez.MediaControl1 interface:

$ dbus-send --print-reply --system --dest=org.bluez /org/bluez/hci0/dev_XX_XX_XX_XX_XX_XX org.bluez.MediaControl1.VolumeUp

dev_XX_XX_XX_XX_XX_XX should be replaced with actual mac address and fdYY is regenerated everytime headphones are connected, there is d-feet software that helps with finding dbus properties

These methods work but according to https://git.kernel.org/pub/scm/bluet.../media-api.txt MediaControl interface is deprecated and MediaTransport should be used instead.
When use Introspect to list available properties:

$ dbus-send --print-reply --system --dest=org.bluez /org/bluez/hci0/dev_XX_XX_XX_XX_XX_XX/fdYY org.freedesktop.DBus.Introspectable.Introspect

I got following response, which contains:

<interface name="org.bluez.MediaTransport1">
...
<property name="Volume" type="q" access="readwrite" />
</interface>

But when trying to list all the properties, Volume is not available:

$ dbus-send --print-reply --system --dest=org.bluez /org/bluez/hci0/dev_XX_XX_XX_XX_XX_XX/fdYY org.freedesktop.DBus.Properties.GetAll string:"org.bluez.MediaTransport1"


   array [
      dict entry(
         string "Device"
         variant             object path "/org/bluez/hci0/dev_XX_XX_XX_XX_XX_XX"
      )
      dict entry(
         string "UUID"
         variant             string "0000110..."
      )
      dict entry(
         string "Codec"
         variant             byte 0
      )
      dict entry(
         string "Configuration"
         variant             array of bytes [
               21 15 02 35
            ]
      )
      dict entry(
         string "State"
         variant             string "active"
      )
      dict entry(
         string "Delay"
         variant             uint16 1500
      )
   ]

I also cannot set the volume:

$ dbus-send --print-reply --system --dest=org.bluez /org/bluez/hci0/dev_2C_41_A1_02_E7_1C/fd29 org.freedesktop.DBus.Properties.Get string:"org.bluez.MediaTransport1" "string:Volume"
Error org.freedesktop.DBus.Error.InvalidArgs: No such property 'Volume'

What is the proper way of setting and reading bluetooth device volume?