There is a field contained within the Azure Cost Management labelled - ResourceName, you will note that this field may be blank within your tenant.
This field ties back to the column with the same name within the raw Azure dataset for EA (Enterprise Agreement) customers, but the column does not exist within the MCA (Microsoft Customer Agreement) dataset.
As Flex Reporting is based of the raw dataset ingested by the platform the field will not be available if you're currently billed under a MCA due to the field not existing within the collected dataset. It will only be available if you are billed via an EA.
If your transition from an EA to a MCA you will note that the field ceases to return a value in the month the transition takes place.