What is the host "xp.apple.com" for and what is sent there?
It seems to be related to the app store and os updates. All my apple devices attempt to connect to it during updates. On MacOS the processes which attempt connection are commerce, appstoreagent, rtcreportingd and App Store.

I would speculate that it is for some kind of telemetry, as I have had it blocked for a couple of months now and it has never caused any updates to fail. I suspect the same is true for configuration.apple.com .