A customer or Provider on customer's behalf cannot place upgrade/downgrade order for a subscription in PBA Control Panel due to the error message saying that conflicting order exists:
Cannot Upgrade/Downgrade Resources for Subscription #1000101: there is already an Upgrade/Downgrade Order #UG000101 in status New(NW). This order prohibits placing an order of the Same Order Type (Per Subscription). Please either cancel conflicting order or wait while it will be processed or contact Provider.
Setting the status mentioned in an error to not prevent other orders placement (Prohibit Order Placing to Don't Prohibit in the order flow) does not make any changes.
PBA has a built-in mechanism which prevents provisioning of conflicting orders, e.g. PBA does not allow to provision upgrade/downgrade order if another non-completed upgrade/downgrade order exists because it is not always clear what amount of resource must be set for a subscription by two non-completed orders, how to bill the customer correctly.
The setting Prohibit Order Placing does not play any role in this case by-design, the check is implemented internally. This information is mentioned in the documentation.
Also, it is not possible to renew subscription if it already has non-completed renewal order.
PBA provides order number of the conflicting upgrade/downgrade order. A customer or Provider may find the order in PBA Control Panel and either cancel it or complete the order provisioning. After the conflict is resolved the customer can place new upgrade/downgrade order for their subscription.