Getting error on installing bootstrap subtheme?
I was getting the same error message and here's how I fixed it.  In your subtheme folder (docroot/themes/bootstrap_subtheme) there's a config folder with two subfolders: install and schema.  Each of these subfolders has a YML file with THEMENAME in the file name, I just changed THEMENAME to my subtheme name and then I was able to install my subtheme.