In the Invoices section, you can see all invoices generated by users or automatically.

You can also create invoices here. Clicking 'Approve' for an invoice will automatically renew the subscriber's subscription

Notes on plan changes

If an invoice is approved for a subscriber on the current plan they are on, then their plan will be extended i.e if their subscription has not expired, they will simply be extended so they do not loose any remaining days. However, if the invoice is for a different plan other than the plan the subscriber is currently on, then the subscription will start afresh from the date of the approval.