Apache mod_proxy to change /location into port

I want to achieve a simple thing - proxy mydomain.com/plex/* into localhost:32400/*. I already have a different proxying rule in place that works fine, but this I cannot get to work.

My sites-enabled config:

<VirtualHost *:80>
    ServerName example.com
    ServerAlias *.example.com

    ProxyRequests Off
    ProxyPreserveHost On

    <Location "/myapp"> ### This works fine, reverse-proxies to a Tomcat server
        ProxyPass http://localhost:8080/myapp
        ProxyPassReverse http://example.com/myapp
    </Location>

    <Location "/plex"> ### This does not work
        ProxyPass http://localhost:32400
        ProxyPassReverse http://example.com/plex
    </Location>

    <Proxy *>
        Order deny,allow
        Allow from all
    </Proxy>
</VirtualHost>

Expected: If I open URL http://example.com/plex/web/index.html, it should be proxied on the server into http://localhost:32400/web/index.html - and that page should be fetched. (opening that localhost address from the server works fine.

What I get: unfortunately all I get is 404 Not Found.

I have found some guides on setting up reverse proxy for Plex (which is what I am trying to do), but they dealt with https, subdomains and others. All I want is a very simple redirection between a location and a port.

Thanks for any help