This can only happen in one of two ways:

  1. You've deleted a driver that has accepted their course licence
  2. The course licence has expired and wasn't renewed if it was a renewable course

In either case, you will need to purchase a new course licence to replace the licence that was deleted or expired. You can add the existing driver again using the form (choose Existing driver and start typing the driver's email or username)

If you accidentally deleted a driver that had started a course, unfortunately, this cannot be undone. If you deleted a driver that hadn't started a course, the course licence would have been added back to your spare licences.