By referring to the link, I secured nginx using Certbot on Ubuntu 22.04.
My domain and it's all subdomains are secured now.
It seems they are using one SSL certificate. Am I right?
But I want to add some subdomains more.
How to do?
My domain is: fivervision.com
you repeat the procedure you followed the first time, including all domain and subdomains you desire (max 100)
you can't add to an existing certificate, but you can issue a new certificate with the domains you want.
if nginx knows about your new domains, you can just run sudo certbot --nginx and read what certbot tells you.
Thanks for your reply.
Yeah, right.
When I ran the command "sudo certbot --nginx", it displays updated list of domains.
My new subdomains are involved there.
Is this the only way?
What do you mean?
I wanted to know if there is any other way, so I asked.
I don't know what to tell you. The only way to add a domain to a certificate is to make a new certificate.
Acme clients can present it differently, but behind the scenes it's the same.
And you can always have a different certificate for each domain.
That's what I want to know. 
Thanks for your help.
All the best! 
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