Most of the time, the user simply needs to restart the device or activate and deactivate airplane mode again, and this usually solves the problem of the unavailable mobile network.However, sometimes it is necessary to re-register the phone and reconnect it with the operator.These solutions for devices that appear as not registered on network, will serve you for both Android and iOS mobiles, and apply to all brands and models of mobiles, including, among others, Nokia, Samsung, iPhone, Motorola, Xiaomi phones, Sony, Blackberry, Apple, LG, Panasonic, Huawei and Sony Ericsson.

https://techcrazee.com/not-registered-on-network/