Cookies aren't being set/overwritten through nginx reverse proxy

Question

For some reason, when I'm proxying my API request through an nginx reverse proxy, my cookies aren't being overwritten with the new values. I've tried adding the following to my nginx config, but I'm not seeing any changes. In this situation, I'm proxying a request from "dev-test.mydomain.com" to "dev-test-backend.mydomain.com".

reverse proxy:

upstream ops_tail_api {
    server 127.0.0.1:8082;
}

in location block:

# Set proxy headers
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host dev-test-backend.mydomain.com;
proxy_set_header X-NginX-Proxy true;

proxy_pass_header Set-Cookie;
proxy_pass_header P3P;

# Handle cookies
proxy_cookie_domain 127.0.0.1 $host;

Am I missing something?