For Custom Tracking Domain to work on Cloudflare, please make sure you have "proxied" disabled:
Please make sure the CNAME entry in CloudFlare is in 'DNS-only' mode (the cloud icon should be gray and not orange).
If the proxy has been disabled, please make sure the record is entered as:
Record type: CNAME
Then, check the propagation on Mxtoolbox.com - enter your Custom tracking domain (inst.yourdomain.com) and choose CNAME lookup:
Make sure that the CNAME record points to Canonical Name prox.itrackly.com
If this is not the case, we encourage you to contact your domain provider to help with record propagation.