Hello,
I created a staging version of my site in SiteGround. I added the records to the subdomain i Cloudflare. SSL shows active for my main domain and sub-domains.
SSL works fine on main domain, but not on my staging subdomain
This video explains what I see: Screen Recording 2021-06-27...
Another issue, your staging13 host does not have a valid certificate on the server but still loads via the proxies, which indicates you’ll have an insecure encryption mode on Cloudflare. Make sure you switch that to “Full strict” and configure a valid certificate for that hostname as well.
The other way round, it should be “Full strict”.
The Universal certificate is fine but it won’t cover the level you posted in your original posting, for that you’d need the $10 a month certificate.