I got error message when i tried to flash image to emmc on rockpi 4b+

I am a new user on rockpi device. I try to flash Debian os image to emmc module. I have rockpi 4b+. It attaches the emmc module on board.
I followed the instruction to burn the image to emmc. But I got the error message “Download image failed” from RKDevTool.
I use rk3399_loader_v1.20.119 as a loader and rockpi4b_debian_buster_xfce4_arm64_20210608_1321-gpt.img as a os image.
How can I do?
please suggest me.

This is an error message that I have.

I just put image in Uboot. It works.

Please, how you do it? Elso see it error, but uboot not help in it… (((
I using rock pi 4 b+