This tutorial is deprecated in favour of Troubleshooting · Cloudflare SSL/TLS docs
Archive
Please note, this tutorial post contains links to external sites. I am not endorsing any external links.
This tutorial post covers the first steps you should take if SSL is working on your main domain, but not on a subdomain.
1. Is there a DNS record for it?
Check the DNS app in your Cloudflare dashboard to see if there is a DNS record there for that subdomain.
2. Check that the DNS record is working correctly
You can use a tool such as https://dnschecker.org, enter the subdomain.domain.com that should be working and check that DNS records are found for it.
3. Check that the subdomain is not too deep
Cloudflare universal certs cover yourdomain.com and *.yourdomain.com, this means they can cover sub.domain.com, but can’t cover www.sub.domain.com or sub.sub.domain.com. If you need a subdomain that isn’t covered by the universal cert, you will need to purchase a dedicated certificate.
There is more information on this at Deprecated - Subdomain too deep
4. Check that the DNS record is set to 
In the DNS app in your Cloudflare dashboard, check that the DNS record for your subdomain is set to , not 
.
5. Check that HTTPS doesn’t work
If you manually enter https://sub.domain.com, does it load with the Cloudflare certificate? If so, you are probably not forcing HTTPS, enable ‘Always use HTTPS’ in the SSL/TLS app of your Cloudflare dashboard.
6. Do you see a certificate from your server?
If you see a cert from your server rather than from Cloudflare, you may be bypassing CF and connecting straight to the server. You can also check for Cloudflare headers in dev tools. If you are not going through Cloudflare, this may be a local caching issue.
If you still need further help, please post the outcomes of these steps and your domain and subdomain and the community can try and help.
Tutorial Reference: CT-10
Reviewed: 07/21
This is a Community Tutorial, most are wiki posts, so can be contributed to by Regulars and MVPs here. If there is a tutorial you would like to see, you can request one here.
If you would like to provide any feedback on this tutorial, please post in the #Meta category, tag your post #TutorialFeedback and let us know the Tutorial Reference above.
Other great resources on this community include the Community Tips . These address best practices when configuring Cloudflare, how to fix issues you may see, and tools to troubleshoot. Also you can view Expert Tips, great posts on the community from people in the know that may help you with your issue.
We encourage users to check out these great resources and the Cloudflare Support Centre before posting