You are likely on a heavily locked carrier firmware. In this case, you may need to use a第三方 tool like or download an .exe updater directly from ZTE's Russian or Chinese support sites (these often get updates first).
) found on the sticker under the device battery or on the back panel. Key Firmware Functions ZTE MF920U 4G WiFi Hotspot, White - Amazon.com.be Zte Mf920u Firmware
Before starting, ensure your device is ready for the process: You are likely on a heavily locked carrier firmware
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