Service for a customer's subscription has the Stopped status. On the 'Service Status History' tab in the subscription properties the following entry is present:
Service Stopping: Automatical Synchronization: Stop Service Triggered by daily billing process
Why PBA stopped the subscription service?
As it is said in the Service Status History the subscription service was stopped by the Daily Billing Process which is executed every day because subscription expired.
Check orders of the subscription in question, most likely the last Renewal Order was not paid in time or was not automatically generated because automatic renewal order generation is disabled for the subscription.
PBA stops the subscription service after subscription period and grace period passed, so check Service Terms which are assigned to the subscription. If Grace Period is 0 days, subscription will be stopped right after expiration, otherwise it will be stopped after grace period is over.
The customer has to renew their subscription to reactivate its service.
You may find more information about Service Terms in the PBA guide: Creating Service Terms.