Why am I getting Proxy returns “HTTP/1.1 407 authenticationrequired”?

I am using nginx, gunicorn, django for backend. I have created apis in django, and these apis works fine for me from postman and even from my python code. But when I try to access the api from proxy server it gives me 'Unable to tunnel through proxy. Proxy returns "HTTP/1.1 407 authenticationrequired."'

Here are my complete issues :
DIGITAL OCEANS : https://www.digitalocean.com/community/questions/why-am-i-getting-proxy-returns-http-1-1-407-authenticationrequired
STACKOVERFLOW : https://stackoverflow.com/questions/44934774/why-am-i-getting-proxy-returns-http-1-1-407-authenticationrequired