So you have gone through the hard work of defining tags and its value for all the resources in Azure portal which you want to make use of them when reporting the costing in PowerBi. Here I will describe how you can expose those tags for billing purposes so that you can filter your costing via tags as well.
First of all we need to get the API access key and enrollment number which you will need to ask whoever that has access to your Enterprise agreement information. You can check if you have access by going to https://ea.azure.com in case someone has given you access. Within the EA portal you will see your enrollment number on the top left of the screen which you will need to note down. To get the API access key you will need to click on "reports" then go to "Download Usage > API Access Key". You will see two keys, make sure you have a look at the effective date (remember US date format). Once you have decided which key to use then click on "expand key" and select "copy" to capture the whole key. If both has expired then clic on "regenerate" for one of them.
Now that you have both the enrollment number and API access key then we can move on to working within PowerBi desktop version. The version I will be using is dated as October 2020 (2.86.902.0 64 bit)
When you start up PowerBi desktop if you get the start up screen then select get data otherwise on the menu bar select "Get Data > More"
This should open up a new window and select "Online Services" followed by "Microsoft Azure Consumption Insights (Beta)" then select "Connect"
To keep it simple I will just select the "UsageDetails" table and click "Load". Now wait for the data to be downloaded which could take some time.
So now you can build queries and make use of the tag values that you have defined for your resources in your subscriptions.