When attempting to build a perspective for cost reports, please use "BigQuery Billing Line Item" as this will pull Financial data based on the labels included in the BigQuery Billing Export.
The "GCP Taggable Assets" is to build perspectives for use with policies and does not have costs associated.
More information on this process can be found here: https://support.cloudhealthtech.com/hc/en-us/articles/360059330051-When-building-a-GCP-perspective-should-I-use-tags-or-labels-