fatal: clean.requireForce defaults to true and neither -i, -n, nor -f given; refusing to clean

Question

You have to either set requireForce to false in your .gitconfig or use the -f or -i flag with this command.

git clean -f will force to clean the untracked files even if clean.requireForce is set to true which is default.
git clean -i will give you an interactive way for cleaning each file
git clean -n will just show which files will be removed if you perform git clean.

Reference: https://git-scm.com/docs/git-clean