The internal bootloader cannot reconcile the different optical transceiver instructions. Always verify your device's exact suffix on the physical underside sticker before proceeding. The Reality of Official ZTE Firmware Links
If you want the direct link to the firmware that your specific device wants, you don't need to search the web. You need to .
Before starting, ensure your PC is connected via an to avoid disconnection during the flash. ZXHN F670L datasheet.pdf - GPON ZTE