Custom location for PGAdmin redirect to 'localhost/' nginx

I have a nginx server with a nodejs API on 'localhost/api' and PGAdmin4 on 'localhost/'. In this case everything works without problem, but as soon as I configure the location of PGAdmin4 in the nginx.conf on 'localhost/pgadmin4', when I click on the login button on the PGAdmin4 interface, I am redirected to 'localhost/' and do not access therefore to PGAdmin.

I have tried several solutions found here, but nothing works ..

Here is my nginx.conf file (pgadmin in proxy_pass is defined in my docker-compose.yml):

user  nginx;
worker_processes auto;

error_log  /var/log/nginx/error.log warn;
pid        /var/run/nginx.pid;

events { worker_connections 1024; }

http {

  include       /etc/nginx/mime.types;
  default_type  application/octet-stream;

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

  access_log  /dev/null;

  upstream app {
    least_conn;
    server app:3000 weight=10 max_fails=3 fail_timeout=30s;
  }

  sendfile        on;
  #tcp_nopush     on;

  keepalive_timeout  65;

  #gzip  on;

  server {
    listen 80;

    location /api/ {
      proxy_pass http://app;
        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;
    }

    location /pgadmin {
      proxy_pass http://pgadmin;
        proxy_http_version 1.1;
      proxy_set_header X-Script-Name /pgadmin;
      proxy_set_header Upgrade $http_upgrade;
      proxy_set_header Connection 'upgrade';
      proxy_set_header Host $host;
      proxy_cache_bypass $http_upgrade;
    }
  }
}