Using conda install with a proxy may result in the following error:

ProxyError: Conda cannot proceed due to an error in your proxy configuration.
Check for typos and other configuration errors in any ‘.netrc’ file in your home directory,
any environment variables ending in ‘_PROXY’, and any other system-wide proxy
configuration settings.

Solution:
Input the command:env | grep -i "_PROXY" and here is the outcome:

HTTP_PROXY=http://http://localhost:8888/
https_proxy=http://http://localhost:8888/
http_proxy=http://http://localhost:8888/
no_proxy=localhost,127.0.0.0/8,::1
NO_PROXY=localhost,127.0.0.0/8,::1
HTTPS_PROXY=http://http://localhost:8888/

Then enter the command unset to delete these agents:

unset  https_proxy
unset  http_proxy
unset  no_proxy
unset  HTTPS_PROXY
unset  HTTP_PROXY
unset  NO_PROXY

Then enter CONDA installation command to solve the problem successfully