Symptoms
It is impossible to list subscriptions of the resellers' customers in the Provider Control Panel in the PBA 5.5.
It is possible to list orders of resellers' customer at Operations > Orders > All Orders, it is possible to list resellers' customers at Operations > Customers > All Customers.
There is no similar screen 'All Subscriptions' at Operations > Subscription in the PBA 5.5.
Resolution
The requested functionality is going to be added in the future versions of PBA in scope of the request PBA-53164.