SSL i use Paid-SSL (Comodo-Possitive) for maindomain.com - can i use Self-Signed SSL for sub.domain.com

Centmin Mod 123.09beta01 and newer can just issue web browser trusted Letsencrypt SSL certificates for your domain and subdomain sites

There's generally 3 ways of setting up HTTPS SSL certificate for Centmin Mod Nginx HTTP/2 based HTTPS

Method 1. The traditional way via centmin.sh menu option 2, 22 but ensuring you set LETSENCRYPT_DETECT='y' in persistent config file created at /etc/centminmod/custom_config.inc before you run centmin.sh menu option 2 or 22 for wordpress. You can do that using command below - only need to do this step once and every subsequent run of centmin.sh menu option 2 or 22 will have letsencrypt ssl certificate support enabled

Code (Text):

# enable letsencrypt ssl certificate integration https://centminmod.com/acmetool/
touch /etc/centminmod/custom_config.inc
echo "LETSENCRYPT_DETECT='y'" >> /etc/centminmod/custom_config.inc

Method 2. Using and testing Centmin Mod 123.09beta01's new addons/acmetool.sh addon which is still in beta testing only for integrating Letsencrypt SSL certificates. And has both auto and manual methods.

Method 3. Fully manual method for free Letsencrypt SSL certificates.

• For existing non-HTTPS Nginx vhost sites migration to HTTPS as outlined at Migrating Existing Nginx Vhost From HTTP to HTTP/2 based HTTPS With Letsencrypt SSL Certificates
• For brand new Nginx vhosts not yet created on server use this guide Using Centmin Mod acmetool.sh addon for Nginx HTTP/2 based HTTPS with free Letsencrypt SSL certificates