Flask + NGINX + Linode gives 502 - Bad Gateway everytime - nginx

Question

I know that there are lots of questions on this topic, but I don't think any of them helped me resolve it.
So, here is my /etc/nginx/sites-enabled/app file
server {
listen 80;
server_name {LINODE_IP_ADDRESS};
location / {
proxy_pass http://127.0.0.1:8000;
proxy_set_header Host $host;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
}
}
And here is my /etc/supervisor/conf.d/app.conf file
[program:app]
directory=/var/www/app
command=gunicorn --workers=3 wsgi:app --limit-request-line 10000
autostart=true
autorestart=true
stopasgroup=true
killasgroup=true
stderr_logfile=/var/log/app/app.err.log
stdout_logfile=/var/log/app/app.out.log
I always get 502 Bad Gateway when I hit Python handler that does redirect(). I can visit the pages that are statically generated with render() function, but anytime redirect() in Flask is executed, I get 502
This is what I get from /var/log/nginx/error.log
2022/08/29 16:44:23 [notice] 43608#43608: signal process started
2022/08/29 16:47:27 [error] 43609#43609: *2 upstream sent too big header while reading response header from upstream, client: 178.222.210.17, server: {LINODE_IP}, request: "GET / HTTP/1.1", upstream: "http://127.0.0.1:8000/", host: "{LINODE_IP}"
2022/08/29 16:50:29 [notice] 44141#44141: signal process started
2022/08/29 16:50:45 [error] 44142#44142: *68 connect() failed (111: Connection refused) while connecting to upstream, client: 178.222.210.17, server: {LINODE_IP}, request: "GET / HTTP/1.1", upstream: "http://127.0.0.1:5000/", host: "{LINODE_IP}"
2022/08/29 16:50:45 [error] 44142#44142: *68 connect() failed (111: Connection refused) while connecting to upstream, client: 178.222.210.17, server: {LINODE_IP}, request: "GET /favicon.ico HTTP/1.1", upstream: "http://127.0.0.1:5000/favicon.ico", host: "{LINODE_IP}", referrer: "http://{LINODE_IP}/"
2022/08/29 16:50:46 [error] 44142#44142: *68 connect() failed (111: Connection refused) while connecting to upstream, client: 178.222.210.17, server: {LINODE_IP}, request: "GET / HTTP/1.1", upstream: "http://127.0.0.1:5000/", host: "{LINODE_IP}"
2022/08/29 16:50:46 [error] 44142#44142: *68 connect() failed (111: Connection refused) while connecting to upstream, client: 178.222.210.17, server: {LINODE_IP}, request: "GET /favicon.ico HTTP/1.1", upstream: "http://127.0.0.1:5000/favicon.ico", host: "{LINODE_IP}", referrer: "http://{LINODE_IP}/"
Can someone please help me understand and fix this? Thanks!