In order to integrate POA and PBA the following packages have to be installed on POA UI server:
- billing_manager (type: cp)
- billing_manager_branding (type: cp, only in case branding service will be used)
However, there is no way to install those packages to UI server because Web Server NG does not have the 'Packages' tab in POA Provider Control Panel.
This problem has been already reported as POA-79404 to the Development Team and resolved in POA 5.5 Update 1.
Update POA to 5.5.1, contact the Parallels Support Team to schedule update installation.