Hi @kamal5chhirang,
The DNS settings don’t quite seem to tie up with what I am seeing. Your screenshot shows them all 
, but for both the root domain and subdomain you mentioned, they seem to be 
, which is good - that means Cloudflare is enabled on the site.
You are right to have SSL not set to Flexible, it should ideally be Full (strict). When I load the subdomain over HTTPS, I get a 521 error, which would suggest that the server is not configured tor HTTPS on that subdomain. You will need an SSL certificate on that server and it will need to be configured to use HTTPS.