Bootcamp problem

Hi I have a problem..(I'm italian and sorry for my english)

I tried to install the updated windows 10 ISO downloaded from the Microsoft website but at the process of copying the files I receive this message: "unable to create the bootable USB drive, the disk does not have enough free space".

I have already tried to contact the Italian apple support and they have unfortunately helped me without success, can anyone help me?

I state that I already have the updated software(10.14.3), a 16GB USB and a free 700GB memory on the disk