Step-3 : Grant permissions at project scope
Prior to proceeding with the following steps, make sure to choose the project from the top dropdown menu that you had previously selected in Step-1: Enable Billing Export. or if you have an existing export, locate the project where the export is saved and choose that project from the top dropdown menu.
Go to IAM
Click on Grant Access
Enter service account id under the new principals.(To get the Service account id follow instructions outlined in this page Retrieve the Service Account Id)
Add Viewer Role
Click on Save