Self-signed certificate gives error “x509: certificate signed by unknown authority”

I am getting this error while trying to pull an image. I am trying to execute the following command from an instance from a private subnet in AWS.I believe the connection outside is via a proxy. Appreciate your help.

sudo docker pull store/intersystems/irishealth-community:2020.

Here is the exact error:

Error response from daemon: x509: certificate signed by unknown authority