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Look at the sticker on the bottom or back of your device (e.g., ZTE F660, ZXHN H298N).
If your router fails to boot, some ZTE models support emergency recovery. Update Zte Router Firmware
You likely downloaded the wrong version for your hardware revision. Check the sticker on the router for a "Ver" or "Hardware Version" number (e.g., v1.0 vs v2.0). Look at the sticker on the bottom or back of your device (e