UNetbootin not detecting mounted USB?

Just mount your drive:

 sudo mount /dev/sdb1 /mnt    

This is what worked for me

1. Delete partition in sdb1 in Gparted.
2. Reformat.
3. In terminal, type sudo mount /dev/sdb1 /mnt.
4. Run UNetbootin as normal.

original answer from maxter (https://forums.linuxmint.com/viewtopic.php?t=165389)

from command line type:

sudo unetbootin installtype=USB targetdrive=/dev/sdX

unetbootin GUI will open with the selected drive already setted, also if it is ntfs formatted.

Try this (worked well in my case):

1. (while Unetbootin is open and iso file mounted)
2. open GParted, go to GParted menu, select Devices and tick the path to your USB (/dev/sdb1)
3. Unetbootin should now recognize your USB drive and proceed with copying.
4. (you will perhaps need to eject and reinsert your USB before)