Hi Jenn, to be able to delete a subscription you must be the owner of the subscription, and the error you are getting means you don't have the right previlages to perform that actions.
to be able to delete your subscription you should elevate your permission
you can follow the below link for details
https://learn.microsoft.com/en-us/azure/role-based-access-control/elevate-access-global-admin
https://learn.microsoft.com/en-us/azure/cost-management-billing/manage/cancel-azure-subscription
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