The pip.conf file should have the following setting pinting the group repo. Notice the pypi and simple at the end of the URL:
[global]
index = http://localhost:8081/repository/pypi-all/pypi
index-url = http://localhost:8081/repository/pypi-all/simple
https://support.sonatype.com/hc/en-us/articles/115000572308-Unable-to-install-PyPi-package
