When a new hosting service is created within WHMCS panel with Plesk Automation plugin, the subscription is created in Plesk Automation but it's incomplete: webspace along with mail and hosting services is not created, just DNS zone.
Plesk Automation 11.5 has a multiple web-space feature. It means that one subscription may have few webspaces. The amount of available webspaces is defined by the limit of a resource such as Apache Webspace or IIS Webspace in the service template.
This feature is incompatible with WHMCS Plesk Automation module.
The webspace can be created manually later by the customer, from within the Plesk Automation Customer Control Panel.
In order to enable automatic webspace provisioning, change the limit of the resource Apache Webspace / IIS Webspace to 1 in the corresponding service template.