Unable to enter RUU mode [oem rebootRUU]

Hi, I have my old Butterfly x920D,
I want to flash firmware to update it, but I realised Im unable to enter ruu mode.

F:\adb-fastboot-win>fastboot oem reboot
...
(bootloader) [ERR] Command error !!!
OKAY [ 0.012s]
finished. total time: 0.013s

F:\adb-fastboot-win>fastboot getvar all
(bootloader) version: 0.5
(bootloader) version-bootloader: 1.57.0000
(bootloader) version-baseband: 3A.32.306.04
(bootloader) version-cpld: None
(bootloader) version-microp: None
(bootloader) version-main:
(bootloader) version-misc: PVT SHIP S-OFF
(bootloader) serialno: FA32TPN00xxx
(bootloader) imei: xxxxxxxxxxxxxxxxxxxx
(bootloader) meid: 00000000000000
(bootloader) product: deluxe_ub1
(bootloader) platform: HBOOT-8064
(bootloader) modelid: PL9911000
(bootloader) cidnum: 11111111
(bootloader) battery-status: good
(bootloader) battery-voltage: 3757mV
(bootloader) partition-layout: Generic
(bootloader) security: off
(bootloader) build-mode: SHIP
(bootloader) boot-mode: FASTBOOT
(bootloader) commitno-bootloader: dirty-ae8bbb39
(bootloader) hbootpreupdate: 11
(bootloader) gencheckpt: 0
all: Done!
finished. total time: 0.097s


Anyone knows why I keep getting the command error?

S-off and Unlocked Bootloader.

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