[rv1103g] Opening loader failed, exiting download boot!

[inisider]

I am trying to use rkdeveloptool to flash Luckfox Pico Plus's uboot but it is failing on DownloadBoot stage. After I run the command:
$ rkdeveloptool db ./rkbin/bin/rv11/rv1103b_usbplug_v1.00.bin

The following message is printed:
Opening loader failed, exiting download boot!

It happens because uiTag is different from what rkdeveloptool is expected:

		PSTRUCT_RKBOOT_HEAD pBootHead;
		pBootHead = (PSTRUCT_RKBOOT_HEAD)(m_BootData);
		if (( pBootHead->uiTag!=0x544F4F42)&&(pBootHead->uiTag!=0x2052444C))
		{
			bCheck=false;
			return;
		}

And first bytes of rv1103b_usbplug_v1.00.bin.bin are:

$ hexdump ./rkbin/bin/rv11/rv1103b_usbplug_v1.00.bin | less
0000000 0081 ea00 0000 0000 5352 4b41 01f8 0000

I checked some other .bin files and they don't have uiTag = 0x544F4F42 or 0x2052444C.

Could someone please provide me any pointers how to resolve that?

Thanks in advance!