Unfortunately your Kindle needs to be registered to do this, and it's often a phenomenal pain in the ass to get old Kindles to register, if it's possible at all

Unfortunately your Kindle needs to be registered to do this, and it's often a phenomenal pain in the ass to get old Kindles to register, if it's possible at all. I've got two old Paperwhites and I can't get either of them to register despite trying for hours and hours with every troubleshooting step I've found.