Add a clarification note to the REST API billing usage documentation (#59209)

Author: sophietheking

content/rest/billing/usage.md

@@ -10,4 +10,13 @@ autogenerated: rest
 allowTitleToDifferFromFilename: true
 ---
 
+The endpoints on this page return usage that is billed to the account associated with the endpoint. For help deciding which level of usage to report on, see [AUTOTITLE](/billing/tutorials/automate-usage-reporting#step-1-decide-what-level-to-report-on).
+
+* User endpoints return {% data variables.product.prodname_copilot_short %} usage that is billed directly to an individual user’s personal account. These endpoints are only applicable if the user has purchased their own {% data variables.product.prodname_copilot_short %} plan.
+* If a user’s {% data variables.product.prodname_copilot_short %} license is managed and billed through an organization or enterprise, their usage is not included in user-level endpoints. In that case, you must use the organization- or enterprise-level endpoints instead.
+
+{% ifversion fpt %}To view enterprise-level endpoints, select the dropdown menu at the top of the page and switch from Free, Pro, & Team to {% data variables.product.prodname_ghe_cloud %}.
+
+{% else %}To view user- and organization-level endpoints, select the dropdown menu at the top of the page and switch from {% data variables.product.prodname_ghe_cloud %} to Free, Pro, & Team.{% endif %}
+
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