I created a subscription using PPA API method
"pem.activateSubscription". What I want now is to add a additional domain for the user. Is there an API function that I can use for that?
Parallels Plesk Automation is the system which is based on two products - Parallels Automation and Parallels Plesk Panel.
Parallels Plesk Panel engine is used to manage hosting, thus you should refer to Plesk Panel API documentation if you want to create additional domains.