zEitEr
Super Moderator
Once any domain, subdomain is added at anytime if SSL is "switched" on (should be by default) The system just automatically goes and creates and installs the cert for the domain. Then notifies the User and or the admin of error and or completion.
If the cert does not complete and or install fully for say dns issues it should retry every few hours automatically.
...and here you hit a limit from Let's Encrypt and will get a temporary ban of your IP. I believe it is not what we want here. Probably it can be solved via utilizing --dry-run, so called staging environment: https://letsencrypt.org/docs/staging-environment/ with higher Rate Limits. The letsencrypt.sh script from DirectAdmin can use staging by the way....