Kt20ymultiv20 Update

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| Error Message | Likely Cause | Resolution | |---------------|--------------|-------------| | DFU device not found | Bootloader mode not entered correctly | Repeat BOOT pin sequence; ensure USB cable supports data (not charge-only) | | CRC mismatch at 0x1A0F | Corrupt .bin file | Re-download the firmware; disable antivirus temporarily | | Timeout on sector erase | Faulty flash memory sector | Run AT_FLASH_REMAP from bootloader (advanced) or contact support | | WDT reset during flashing | Watchdog not disabled | Before bootloader mode, send AT+WDOG=0 from serial console | kt20ymultiv20 update