Nginx Reverse Proxy do not load JS and CSS from other server

I have two version of a WebApp, running on two different servers (prod and dev). Prod version is available on exemple.com, and dev version on exemple.com/dev. However, when I set the proxy to load dev version, only the index.html file is loaded, JS and CSS are not loaded.
If I check the request url in devtools, I see that index.html comes from https://exemple.com/dev while main.bundle.js comes from https://exemple.com/

Here is the nginx.conf for prod server

server {
        listen       80 default_server;
        #listen       [::]:80 default_server;
        server_name  _;
        root         /site/app;

        # Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        location /api/ {
                proxy_pass http://127.0.0.1:3000/api/;
                proxy_http_version 1.1;
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection 'upgrade';
                proxy_set_header Host $host;
                proxy_cache_bypass $http_upgrade;
                add_header 'Access-Control-Allow-Origin' '*' always;
                add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS' always;
                add_header 'Access-Control-Allow-Headers' 'Origin, X-Requested-With, Content-Type, Accept, authorization' always;
                add_header 'Access-Control-Allow-Credentials' 'true' always;
        }

        location /dev {
                proxy_pass http://10.10.38.18/;
                proxy_http_version 1.1;
                proxy_cache_bypass $http_upgrade;
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection 'upgrade';
                proxy_set_header Host $host;
        }

And here for dev server:

server {
        listen       80 default_server;
        #listen       [::]:80 default_server;
        server_name  _;
        root         /site/webApp;

        # Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        location / {
                autoindex on;
        }
        location /api/ {
                proxy_pass http://127.0.0.1:3000/api/;
                proxy_http_version 1.1;
                proxy_set_header Upgrade $http_upgrade;
                proxy_set_header Connection 'upgrade';
                proxy_set_header Host $host;
                proxy_cache_bypass $http_upgrade;
                add_header 'Access-Control-Allow-Origin' '*' always;
                add_header 'Access-Control-Allow-Methods' 'GET, POST, OPTIONS' always;
                add_header 'Access-Control-Allow-Headers' 'Origin, X-Requested-With, Content-Type, Accept, authorization' always;
                add_header 'Access-Control-Allow-Credentials' 'true' always;
        }