Symptoms

Unable to place downsizing or cancellation requests for subscriptions during the Microsoft cancellation window. From the end-customer or reseller Control Panel, the following error message is displayed when trying to change the subscription. 

 According to the terms of service, this subscription cannot be downsized.

Cause

The issue is caused by the software related issue with id #OA-35327. 

Resolution

A permanent solution will be implemented in the scope of #OA-35327.

Nevertheless, there is a workaround in case a customer places a change order on MSFT. Please, refer to How to cancel Microsoft365 NCE PLM based subscription before the end of subscription period.