Only Plesk Administrator can create site aliases via API RPC. To create a site alias, it is enough to specify the site ID and the site name.
You can also specify alias settings when creating a site 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 site alias settings can be set on a particular server, use the get-supported-services operation.
Please send us your feedback on this help page.