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