You don't own the directory you're trying to move files into:
/Users/Username/...
is a user owned directory, so you're allowed to manipulate files there./Library
is not a user owned directory.
In order to manipulate files in a non-user owned directory you would need elevated permissions. Instead of using /Library
you should be using ~/Library
, which is the user owned directory. ~/Library
is the shorthand name for /Users/Username/Library
.