Hello!
Currently, I am looking for a way of getting billable cost per campaign.
It looks like right now it's not a part of GAQL, because there is no mention regarding that in the documentation here -- [
https://developers.google.com/google-ads/api/reference/rpc/v8/overview?hl=en](URL).
It can be retrieved in Invoice, which is looking kinda weird, because if there is a difference on the campaign/campaign_report actual cost that will be invoiced, it will be better to have access to the campaign performance report or campaign budget report, but right now there is not any way to get through GAQL request.