In the Merchant Backend, either customer access can be blocked completely (this also blocks product access) or product access can be blocked for individual subscriptions/products. Both blocks can be removed manually in the Merchant Backend in the customer account.
1. Product access blocked
Open the customer account.
Open the corresponding subscription.
Access can be unblocked again in the action bar.
2. Customer access blocked
Open the customer account.
Access can be unblocked again in the action bar.