I’ve setup Nginx with reverse proxy to my django backend api. The requests from Postman work perfectly fine but on Flutter I get a HTTP 400 157 from the nginx server while performing a GET request.

Upon inspecting the log , I see the following :

client sent invalid header line: "x3a..." while reading client request headers

Here is my nginx.conf.

worker_processes auto;
events {
    worker_connections 1024;
}

http {

    log_format custom '$remote_addr - $remote_user [$time_local] "$request" '
    '$status $body_bytes_sent "$http_referer" '
    '"$http_user_agent" "$http_x_forwarded_for" $request_time';

    #Note that these are defined outside of the server block altho they don't necessarily need to be
    proxy_cache_path /tmp/nginx levels=1:2 keys_zone=my_zone:10m inactive=60m;
    proxy_cache_key "$scheme$request_method$host$request_uri";


    default_type application/octet-stream;

    include /etc/nginx/mime.types;

    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    keepalive_timeout 65;
    types_hash_max_size 4096;
    
    
    upstream my-django-rest-api {

        server 172.16.16.1:8080; # The internal Django API service
    }

    server {
        listen 1652;

        # Access & Error Logs
        access_log /var/log/nginx/access.log custom;
        error_log /var/log/nginx/error.log;

        location / {
            proxy_pass http://my-django-rest-api;
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Forwarded-Proto $scheme;
            
            proxy_cache my_zone;
            add_header X-Proxy-Cache $upstream_cache_status;
            proxy_buffering on;
            proxy_cache_valid 200 302 60m;
            proxy_cache_valid 404 1m;

            # WebSocket support (nginx 1.4)
            proxy_http_version 1.1;
            proxy_set_header Upgrade $http_upgrade;
            proxy_set_header Connection "upgrade";
        }
    }
}

What Do I need to do on the Nginx end before I start troubleshooting
it from the Frontend ?

What exactly is “x3a…” which is termed as Invalid in header line?