Boot Camp: "Your bootable USB drive could not be created. There is not enough space available on the disk."

My mac is on High Sierra and so for using Boot Camp to install Windows I'm using an external flash drive with 32 GB storage. However, whenever I try to install the Windows iso and the other required stuff into the flash drive, it keeps on giving me this error. Anyone please help so I can fix it? Also, what disk are they talking about that doesn't have enough space available? I'm really not an expert at these things.

Thanks, silo15.