I ran this script on my Ubuntu VM machine.

I ran:
sudo ./mkeosdrive /dev/sdb ~/Downloads/ER-e100.v2.0.9-hotfix.7.5622762.tar
Output was:

umount: /dev/sdb1: not mounted.
no filesystem mounted from /dev/sdb
Press any key to continue formatting /dev/sdb
or hit Ctrl+C to exit now...
1+0 records in
1+0 records out
512 bytes copied, 0.00622698 s, 82.2 kB/s
Waiting for disk sync...
Waiting for disk sync...
Formatting /dev/sdb partitions...
mkfs.fat 4.1 (2017-01-24)
mkfs.msdos: unable to open /dev/sdb1: No such file or directory

I suspected the system hadn't recognized the partition yet by the time the mkfs.msdos command was run.

I added:

# Add a delay to allow the system to recognize the new partitions
sleep 2

Approximately line 83, between echo "Waiting for disk sync..." Line 81 and echo "Formatting $DEVICE partitions..." Line 84

After the 2 second sleep was added everything completed normally.

I'd suggest you perhaps consider added that 2 second sleep.

Finally you had a minor typo line 27: echo "If you want to provide a root partition end cap size but no config, use \"-\" without the quotes as the third paramenter."

Should be say parameter

At first I tried to use a 1GB disk and it failed because the size was actually 940MiB or something. I ended up just using a 4GB USB. I'm not sure what the solution is, perhaps it's too small?

Otherwise great script thanks.