Thank you for asking.
I am sorry you are experiencing an issue with your sub-domain while using Cloudflare.
When I do a lookup, unfortunately I cannot find any DNS record related for your sub-domain aptrack.jobwarehouse.co.uk. Seems to me like it’s missing. See below related article:
Could you check the DNS tab at Cloudflare dashboard for your domain name and add a missing hostname? Instructions from below article can help you how to add it:
Before moving to Cloudflare, was your Website working over HTTPS connection?
Maybe you do not have a valid SSL certificate installed for your sub-domain at your origin host/server?
You could determine this by:
Use the “Pause Cloudflare on Site” option from the Overview tab for your domain at dash.cloudflare.com .
The link is in the lower right corner of that page.
Give it five minutes to take effect, then make sure site is working as expected with HTTPS.
Only then should you un-pause Cloudflare and double-check your SSL/TLS setting to make sure it’s Full (Strict).
May I ask what SSL option have you got selected under the SSL/TLS tab at Cloudflare dashboard for your domain ( Flexible, Full, Full Strict … )?
Here is a way to re-check if you correctly setup the SSL for your domain with Cloudflare:
In case you do not have an SSL certificate, you can use Cloudflare SSL, if so, kindly make sure you follow the instructions as follows on the below article to setup an SSL certificate using Cloudflare Origin CA Certificate:
