SSL Not working: for domains hosted in AWS Route53

Hello,

Below is my setup:
I have a domain with SSL in the Cloudflare. Let’s call it as *.abc.com

I have a web app hosted on AWS EC2, behind the load balancer. The load balancer with AWS Certificate is pointed out to an internal domain using Route53 for our internal use. Let’s call it as https:// xyz. stg. abc. com (Adding space due to new user restrictions to break the links)

Now, I want to expose that internal domain(https:// xyz. stg. abc. com) (Adding space due to new user restrictions to break the links) to the external world via Cloudflare by setting a CNAME Name as xyz. abc. com (Adding space due to new user restrictions to break the links) and its content value as xyz.stg.abc.com

When I access https://xyz.abc.com, The traffic is passing properly as the webpage is loading up and I can see entries in my servers Nginx logs too.

But, HTTPS is not working and it prompts me that the site is insecure. How to fix this issue?

Could this be due to a multi-level subdomain?

Thanks in Advance,
Krishna.