You're Owner on the subscription but you still need to enable the below:
To enable an option in the Azure portal:
- Sign in to the Azure portal at https://portal.azure.com with an enterprise administrator account.
- Select the Cost Management + Billing menu item.
- Select Billing scopes to view a list of available billing scopes and billing accounts.
- Select your Billing Account from the list of available billing accounts.
- Under Settings, select the Policies menu item and then configure the setting.