How to generate a raw UBI image with 2 UBI volumes?

I am working on an embedded Linux (kernel-5.24), where UBIFS is used as filesystem for both rootfs and user configuration data. Now I am trying to generate one single UBI image to burn the NAND FLASH (128MB) directly from within factory. As I said, there are 2 UBI volumes in my system, one is rootfs (rootfs.ubifs), the other is for user configuration (usrconf.ubifs), and the ubinize.cfg is as follows,

[ubifs_volume]
mode=ubi
image=rootfs.ubifs
vol_id=0
vol_size=56MiB
vol_type=dynamic
vol_alignment=1
vol_name=rootfs

[usrconf_volume]
mode=ubi
image=usrconf.ubifs
vol_id=1
vol_size=56MiB
vol_type=dynamic
vol_alignment=1
vol_name=usrconf
vol_flags=autoresize

Now my question is how to combine the rootfs.ubifs file and usrconf.ubifs file into one rawubi.img to burn the FLASH? Where should I put the 2 files into the final rawubi.img? == Updated with more tests == I changed the ubinize.cfg as follows (set usrconf volume to static and vol_id=0, rootfs volume as vol_id=1)

[usrconf_volume]
mode=ubi
image=usrconf.ubifs
vol_id=0
vol_size=56MiB
vol_type=static
vol_alignment=1
vol_name=usrconf

[ubifs_volume]
mode=ubi
image=rootfs.ubifs
vol_id=1
vol_size=56MiB
vol_type=dynamic
vol_alignment=1
vol_name=rootfs
vol_flags=autoresize

ubinize -m 2048 -p 128KiB -s 512 -O 2048 ./ubinize.cfg -v -o rawubi.img After burned the generated rawubi.img to NAND FLASH, I booted the Linux with root=ubi0:rootfs rootfstype=ubifs, and hit following error,

[    2.671151] UBIFS (ubi0:1): Mounting in unauthenticated mode
[    2.677163] UBIFS (ubi0:1): background thread "ubifs_bgt0_1" started, PID 70
[    2.706562] UBIFS error (ubi0:1 pid 1): ubifs_read_node: bad node type (255 but expected 9)
[    2.715237] UBIFS error (ubi0:1 pid 1): ubifs_read_node: bad node at LEB 187:115776, LEB mapping status 0
[    2.725139] Not a node, first 24 bytes:
[    2.725148] 00000000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff

It seemed that the FLASH is NOT populated with the data of rootfs.ubifs when rootfs volume is changed to vol_id=1.