pulseaudio – Terminal command to increase the volume to 100% for another user using SSH?

Basically I’m remoteing into an Ubuntu system using SSH using a user account name test and want to increase the system volume to 100% for another currently logged in user called john. When I run this command I get the following error (see below). What’s the proper way to increase the volume of another logged in user using an Ubuntu system?

test@asuslinux:~$ sudo -u john pactl -- set-sink-volume 0 100%
Connection failure: Connection refused
pa_context_connect() failed: Connection refused
test@asuslinux:~$