Domain name (agtherm.local) invalid, because "not valid public suffix"

[cdarsac]

Hello,
My domain name "AGTherm.local" is not correct, because it has not a public suffix.
But it's my only "domain name".
*what should I do?

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Please fill out the fields below so we can help you better. Note: you must provide your domain name to get help. Domain names for issued certificates are all made public in Certificate Transparency logs (e.g. crt.sh | example.com), so withholding your domain name here does not increase secrecy, but only makes it harder for us to provide help.

My domain is: agtherm.local

I ran this command: certbot --apache

It produced this output:
root@Ubuntu-GLPI:~# certbot --apache -v
Saving debug log to /var/log/letsencrypt/letsencrypt.log
Plugins selected: Authenticator apache, Installer apache
Please enter the domain name(s) you would like on your certificate (comma and/or
space separated) (Enter 'c' to cancel): agtherm.local
Requesting a certificate for agtherm.local
An unexpected error occurred:
Error creating new order :: Cannot issue for "agtherm.local": Domain name does not end with a valid public suffix (TLD)
Ask for help or search for solutions at https://community.letsencrypt.org. See the logfile /var/log/letsencrypt/letsencrypt.log or re-run Certbot with -v for more details.
root@Ubuntu-GLPI:~#

My web server is (include version): Apache/2.4.41 (Ubuntu)

The operating system my web server runs on is (include version): Ubuntu 20.04.4 LTS

My hosting provider, if applicable, is:

I can login to a root shell on my machine (yes or no, or I don't know): Yes

I'm using a control panel to manage my site (no, or provide the name and version of the control panel): No

The version of my client is (e.g. output of certbot --version or certbot-auto --version if you're using Certbot): certbot 1.26.0

[9peppe]

@cdarsac

My domain is: agtherm.local

You have to use an actual public domain on the public domain name system, you cannot make one up.

[cdarsac]

Yes, I understand, but I have not a "public Domain Name".

All my users work in a private Domain Name.

[9peppe]

Then you cannot get a publicly trusted certificate, you'll have to work with a private certificate authority.

Private names, private CA.

Public names, publicly trusted CAs.

[cdarsac]

Ok, does that mean I can’t use "certbot"

[9peppe]

The answer is more complicated than you imagine.

You can use certbot but you cannot use Let's Encrypt. You'd have to use certbot with something like smallstep CA: https://smallstep.com/docs/step-ca

[danb35]

@cdarsac

I have not a "public Domain Name".

You could get one, you know. Otherwise, as said, you won't be able to get a cert from Let's Encrypt, because they (like most other certificate authorities) only issue certs for public domain names.

[Osiris]

You can even get free domain names.