I have installed SSL on my server and it's perfectly working. However, when I tried to press
Admin panel > security settings > Enable secure connection in the administration panel
I keep getting this error
WarningThe secure connection check has failed. Please ensure that SSL certificate is installed on your server. Check out the Knowledge base article for more details.
subdomains are counting as separate domain and you need wildcard SSL. The subdomains that you want to use, you must add them in your wildcard so they can work, or get a separate SSL for that subdomain
I don’t use let’s encrypt on live servers and I am not sure, but at dev server it auto detects the domains and adds the SSL certificates after some minutes. I am not sure about subdomains. your issue sounds like that the certificate don’t have the subdomain you have the cs cart.
in cs cart file config.local.php have you checked that at https_host that you have your sub domain?