A server system for updating firmware of a client device in an IoT network receives an indication that the client device has re-registered after being de-registered. The server system determines a current version of firmware and a latest successful status of a FOTA update on the client device. When the current version of the firmware corresponds to a latest version of the firmware available, the server system saves information regarding the latest version of the firmware to its database. When the current version of the client device does not correspond to the latest version of the firmware available, the server system transmits an upgrade package of the FOTA update and an indication of the latest successful status of the FOTA update to the client device. The server system thereby enables the client device to continue the FOTA update from the latest successful status of the FOTA update.