You can use this form to Opt-In to Proportional Attribution of subscription fees for spend-based Committed Use Discount (CUD).  

With proportional attribution, the amount of the subscription fee charged to each project will be proportional to the amount of CUD credit consumed, and any unattributed subscription fee will remain as charged to the billing account level (unattributed to a project).

In order to enable your account for this feature, Google needs to collect the GCP billing account IDs to enable as well as the email address of the user making this request. We need to collect the email address of the user making this request to verify that they have edit permissions for any billing accounts being enabled.

Google Cloud Privacy Notice: https://cloud.google.com/terms/cloud-privacy-notice.