The --dry-run option uses a different server from the real one that does not issue real certificates, known as the staging server.
Some other users on the forum are reporting getting the same error falsely from the staging server:
If things worked fine for the same domain(s) yesterday, you're likely experiencing the same thing and there's nothing wrong with your setup. It will probably work fine tomorrow.
The real server (known as the production server) is reportedly working fine. If you need to issue certificate for real it ought to be working properly.