You may also see a banner across the top of you SEPC Portal when you sign-in stating: "Some of your groups are assigned to subscriptions which have expired. Go to the Subscriptions page and transfer those group to an active subscription. You may need to purchase additional Subscriptions,"
An expired or canceled subscription is applied to your groups instead of the active subscription. You are trying to enroll a device to a group where there are no licenses available or subscription assigned. This typically happens when your account has multiple subscriptions.