Using CalDev at UCS

Hi,
What needs to be configured to use the calendar (DevCal services).
At the moment I have configured via ucs set

com.openexchange.dav.prefixPath=/dav
com.openexchange.dav.proxyPrefixPath=/

Then I added an entry in /etc/apache2/apache2.conf

ProxyPass /.well-known balancer://oxserver/.well-known
ProxyPass /dav balancer://oxserver-sync/dav

When I try to go to http://server/dav/caldav
I get a Service Unavailable 503 error.
In Apache2 logs I see:
[Mon Dec 19 09:04:11.239152 2022] [proxy_balancer:error] [pid 11065] [client 10.0.0.168:6437] AH01171: balancer://oxserver-sync: No workers in balancer

Can someone help me?

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