macOS contact syncing with CardDAV is not retrieving any contacts

[rgov]

I am investigating https://github.com/monicahq/monica/issues/4240 in the Monica project, which uses sabre/dav under the hood.

Using a traffic sniffing tool, I see that macOS makes a request to the CardDAV endpoint with the following query, and a Depth: 0 header:

<?xml version="1.0" encoding="UTF-8"?>
<A:propfind xmlns:A="DAV:">
  <A:prop>
    <B:addressbook-home-set xmlns:B="urn:ietf:params:xml:ns:carddav"/>
    <B:directory-gateway xmlns:B="urn:ietf:params:xml:ns:carddav"/>
    <A:displayname/>
    <C:email-address-set xmlns:C="http://calendarserver.org/ns/"/>
    <A:principal-collection-set/>
    <A:principal-URL/>
    <A:resource-id/>
    <A:supported-report-set/>
  </A:prop>
</A:propfind>

The server gives basically a bunch of <d:supported-report> replies but no contacts. macOS never seems to make a request with a higher Depth header.

Are there other applications that integrate sabre/dav for contact syncing that are confirmed to work with macOS? If so, then the problem may be with Monica.

But otherwise, how can I help to diagnose the issue?