nginx reverse proxy for oracle apex cloud application

I would like the url below to be the proxy for my oracle apex application url which is very long and not friendly.

https://myapp.mydomain.com --> proxy for https://verylongstring.oraclecloudapps.com/ords/r/myws/myapp/

The config that I have is shown below:

server { server_name myapp.mydomain.com;

   location / {     
     proxy_pass https://verylongstring.oraclecloudapps.com/ords/r/myws/myapp$request_uri;
     proxy_set_header Host $host;
     proxy_set_header Origin "";
     proxy_set_header X-Forwarded-Host $host:$server_port;
     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_connect_timeout   600;
     proxy_send_timeout      600;
     proxy_read_timeout      600;
     send_timeout            600;
     proxy_redirect  off;
   }

}

The above didnt work. I got 404 Not Found. Can someone help me?