Question XML API error

[tersor]

We want to automate tasks from Wordpress toolkit via the XML API.
But is seems that managing WordPress installations via XML API is not supported on Plesk 17.x?
Is this correct?

Plesk Onyx version 17.5.3
XML API version 1.6.9.0

The following schemas is present:
$ find . -type f -name "wpinstance.xsd"
./admin/htdocs/schemas/rpc/1.6.7.0/wpinstance.xsd
./admin/htdocs/schemas/rpc/1.6.6.0/wpinstance.xsd

POST:
<packet>
  <wp-instance>
    <get-list/>
  </wp-instance>
</packet>
RESPONSE:
<?xml version="1.0"?>
<packet version="1.6.9.0">
  <system>
    <status>error</status>
    <errcode>1014</errcode>
    <errtext>Parser error: Request is invalid. Error in line 2: Element 'wp-instance': This element is not expected. Expected is one of ( request-settings, server, customer, webspace, subdomain, dns, db_server, mail, migration, certificate ).</errtext>
  </system>
</packet>

When specifying v1.6.7.0:

POST:
<packet version="1.6.7.0">
  <wp-instance>
    <get-list/>
  </wp-instance>
</packet>
RESPONSE:
<?xml version="1.0" encoding="UTF-8"?>
<packet version="1.6.7.0">
  <wp-instance>
    <get-list>
      <result>
        <status>error</status>
        <errcode>1017</errcode>
        <errtext>This feature is not supported anymore.</errtext>
      </result>
    </get-list>
  </wp-instance>
</packet>