What format for Move to USB

Hi,
I’m trying to use the “Move to USB” option, but my USB stick doesn’t seem to be formatted properly.

While the option is running, I get the following message:
/dev/sda1: Created a new partition 1 of type ‘Linux’ and of size 25GiB.

then, later in the run:
mounting new root ‘/dev/sda1’
mount: wrong fs type, bad option, bad superblock on /dev/sda1

Neither of these errors stop the move, but when I try to boot from the card, the boot up stops (sorry, forgot to record that error).

My question is, should this option work with an exfat USB stick? If not, what format should I be using on the USB stick?

Regards,
SteveT

Update:
reformatted using another RPi to vfat. Same result:
end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(8,1)

Here’s the complete log from the Move to USB:

stopping openHAB
1+0 records in
1+0 records out
512 bytes copied, 0.0072061 s, 71.1 kB/s
partitioning on ‘/dev/sda’
Checking that no-one is using this disk right now … OK

Disk /dev/sda: 250 GiB, 268435456000 bytes, 524288000 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Created a new DOS disklabel with disk identifier 0xca8372f1.
/dev/sda1: Created a new partition 1 of type ‘Linux’ and of size 250 GiB.
Partition #1 contains a vfat signature.
/dev/sda2: Done.

New situation:

Device Boot Start End Sectors Size Id Type
/dev/sda1 2048 524287999 524285952 250G 83 Linux

The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.
creating filesys on ‘/dev/sda1’
mke2fs 1.43.4 (31-Jan-2017)
/dev/sda1 contains a vfat file system
Creating filesystem with 65535744 4k blocks and 16384000 inodes
Filesystem UUID: 6dfd8012-4fc5-4747-888d-987758cbc734
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
4096000, 7962624, 11239424, 20480000, 23887872

Allocating group tables: done
Writing inode tables: done
Creating journal (262144 blocks): done
Writing superblocks and filesystem accounting information: done

mounting new root ‘/dev/sda1’
mount: wrong fs type, bad option, bad superblock on /dev/sda1,
missing codepage or helper program, or other error

   In some cases useful info is found in syslog - try
   dmesg | tail or so.

copying root sys, please be patient. Depending on the speed of your USB device, this can take 10 to 15 min


291,938,986  12%    6.53MB/s    0:00:42 (xfr#460, to-chk=0/63603)

adjusting fstab on new root
adjusting system root in kernel bootline


OK, moving system root finished you’re all set, PLEASE REBOOT