Note the space in the directory below. You will notice in the error above the path it tries to find is not the full path, just "space/PublicSans-ExtraLightItalic.font/"


Now the the folder with the name "text space" is "text_space"

Run font copy again and the first message you see is 
Click yes and then you see:

Eliminate any spaces the in folder names of the directory structure your font files are in the you are running Font Copy tool on.

Space in a folder name that is part of the directory structure the font you are trying to copy is in.