I'm new in the community so forgive if this is a known question (but I did not found the solution anywhere)
I was able to get correctly the certificates using DNS challenge, but for a mistake, I deleted the registered domain (is a Dynamic domain example my "domain.org") so I lost the registered CNAME value.
If I try to register the domain again using this command:
I'm assuming you're using the free acme-dns server at https://auth.acme-dns.io? (Which is not really recommended, as you're putting all your trust in a sort of unknown service with regard to whom is allowed to issue certificates for your domain.)
If the above is the case, you could remove /etc/letsencrypt/acmedns.json (or better: rename it so you'll have a backup) and start the on-boarding for the acme-dns-auth.py script again.
I think the reason you weren't getting the value to add to the DNS record is that you didn't need to: the authorization from your first order was still valid, so issuance succeeded immediately without needing to re-do the DNS-01 challenge.
This is also why you hit the duplicate certificate rate limit: each of those times you thought things were failing because you weren't being given a DNS challenge value, they were actually succeeding all the way through issuing the certificate.
The reason why I revoke a certificate it was because I deleted by mistake the Dynamic Domain Name loosing the DNS records associates with it.
Recreating the domain I experienced this message during Let’s Encrypt command: certbot renew —dry-run
Failed to renew certificate mydomain.org with error: Some challenges have failed.
So I start clutching at straws trying to solve the situation keeping the domain name but I exceeded rate limit. In this case because is urgent I had to abandon the original domain name restarting from the beginning with a new name.
As I told I’m newbie on Let’s Encrypt logic: I received other messages during simulated renew about “some challenges have failed” and I’m afraid, crossing my fingers, when the real expiration terms expire.
I’m wondering why Let’s Encrypt, when creating a new certificate, does not send for future reference a simple email containing the CNAME value avoiding I hope, all those trouble.
Because this has nothing whatsoever to do with Let's Encrypt. You're using--for some reason, which you haven't mentioned, and I'm not sure you even understand--a third-party service to handle DNS validation for you. It's that third-party service, not Let's Encrypt, that has you create the CNAME record. Let's Encrypt will follow that CNAME record (it's how acme-dns can handle the validation for you), but doesn't need it, nor does it request you create one--that's all on acme-dns. Which, I repeat, is something completely distinct from Let's Encrypt.