Your phone and PC need to speak the same language. Head to the Device Manager on your PC, uninstall any existing drivers related to your phone or "SPD," and then install the latest Spreadtrum/Unisoc USB drivers. Then, restart your PC to ensure the new drivers are loaded correctly.
For OS updates / firmware downloads:
Troubleshooting the "fdl2 failed" Error: Causes, Solutions, and Prevention fdl2 failed
Flashing firmware requires a highly stable, high-speed data stream. If the Spreadtrum COM drivers are outdated, or if you are using a faulty USB cable or port, data packets for the heavier FDL2 file can drop, breaking the connection mid-process. 4. Locked Bootloader / Secure Boot Interference Your phone and PC need to speak the same language