Problem adding new domain to existing certificate

[turbo]

I just tried to add a new domain to my existing certificate. Looking at the documentation for certbot

--expand If an existing cert covers some subset of the
requested names, always expand and replace it with the
additional names.

I used the following commandline on Debian
$certbot certonly --standalone --rsa-key-size 4096 --expand -d newdomain.com

The process started sucessful and created a NEW cert next to the one I wanted to "expand". Any ideas what I am missing?
I am under the impression, that this command would add the new domain into the current cert and not creating a new additional certificate.

Thank you for any hints.

[Osiris]

Yes, you forgot to name (with -d) the FQDNs of the certificate you wanted to expand.

certbot can’t know to which certificate you want to add the new domain. The idea is you enter the domains of the certificate you’d like to expand and the domain you want it to expand with.

[turbo]

Thank you for this info. I started this post before I noticed the reply in my previous one which answered this at the same time.

Sorry for the kind of “double post”