First please make sure the same endpoint is accessible through a non-Pega rest client, e.g., Postman or Connect-SOAP, from the same machine pega server is running (curl command would do as well). If yes, then upload the entire error log and specify the pega version.

Checked with curl command and see that the connectivity is not happening and going through proxy

Then I have unset the proxy using:

unset https_proxy

unset HTTPS_PROXY (this worked for me. Not sure why running command in lower case did not work)

We can check the proxy using: env | grep -i proxy

After this again checked the connectivity with curl command > Connectivity is success

After this from Pega also conenctivity is success