Use proxy in advanced configuration

[asdfgher sigaint org]

Hello
I have Qubes as os and have thhis configuration

sys-net-->proxyVM-->proxyVM-->AppVM

In the first proxy vm I have a proxy software while in the second I have a
vpn in network manager

My goal is that the vpn "see" proxy software in the first proxyVM. Now I'm
gone to advances-->proxies and write ip of first proxyVM and the port of
software proxy (4001). Unfortunately it doesn't work, is the setup
correct?
Is possible to do it?

Thank you