Technical Description (Comment)
WARNING: This page is about a different car, the 2014 Mitsubishi Outlander. However, it is still accessible from the selected car via links, so may be relevant.
If only some keyless operation keys cannot be registered, the keyless operation key itself may be faulty. If no keyless operation key can be registered, the key assembly may have already been registered for another vehicle, or the KOS-ECU may be faulty.