Only Plesk Administrator can create domain aliases via API RPC. To create a domain alias, it is enough to specify the domain ID and the domain name.
You can also specify alias settings when creating a domain alias (all of them are optional):
You can specify alias settings during or after creation of an alias. Alias settings can be set using the set operation. To get information on which domain alias settings can be set on a particular server, use the get-supported-services operation.