An order to change the service plan failed with an error:
Change Service Plan failed: There is already a Change Order #CHID in Status Completed(CP). This order prohibits the 'Change Plan Period for Subscription' action. Please either cancel conflicting order or wait until it is processed; or contact Provider.
There is indeed an order
CHID, which is successfully completed, all the provisioning items have completed status.
An order to change the service plan was created earlier than order #CHID provisioning completed. Usually it is not possible to place a second change order on the same subscription unless the first one is completed, but there is a bug with id #PBA-57940 ("PlaceResourceUpgradeOrder_API does not detect conflicted upgrade orders") due to which order placement is possible with API.
Cancel the current order to change the service plan and place a new one, it is expected to be completed successfully.