How to detect whether cross domain tracking is working properply?

So i wanted to track conversion in Google Ads. The challenge was that the traffic was sent to domainA whilst the potential conversion happens on domain.

What I did :
– Put on both domains the same Google Analytics code
– Added trusted domains in the Analytics code

<!-- Global site tag (gtag.js) - Google Analytics -->
<script async src=""></script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());

  //gtag('config', 'UA-29307123-1');
  gtag('config', 'UA-29307123-1', {
  'linker': {
    'domains':  ['', '','', '']

Couple of checks:
CHECK 1: If you moving from one domain to another domain one should see something pasted to the target url:
E.g. _ga=2.262824463.2041018120.1646037965-237878360.1646037965

CHECK 2: When visiting urls (no matter if this is on the origin domain or the targetted domain), there is a ‘signal’ sent out to Google with an ID, this ID should be the same. Look at it as if this is a way to identify the same person. When not configuring for cross domain tracking, those ID are by default different.
So how to check?
Open the Developer Console, when visiting a page, go to the Network tab and search for “cid=”

triggered script on the url of source domain (domainA)×1080&vp=673×937&je=0&_u=QCCACUABB~&jid=&gjid=&cid=237878360.1646037965&tid=UA-29307123-1&_gid=2041018120.1646037965&gtm=2ou2n0&z=2112349406
triggered script on url of the target domain (domainB)×1080&vp=673×937&je=0&_u=ACCACEABhAAAAC~&jid=&gjid=&cid=237878360.1646037965&tid=UA-29307123-1&_gid=2041018120.1646037965&_slc=1&z=1894522280

see also