How to mask sub-domain using nginx - nginx

Question

I have nodejs application working with a main domain, and its connecting thought nginx proxy pass to nodejs application, with redirection rule , as per the redirection rule if request is coming from mobile, it will redirect into a sub-domain, it is working fine.
both main domain and sub-domain are different version ,and running deferent server.
Now I want to mask this sub-domain , I don't want to see my sub-domain in browser, how can I do this.
Below mentioned my nginx conf.
server {
listen 80;
server_name mydomain;
return 301 https://$server_name$request_uri;
}
include mime.types;
server {
listen 443 ssl;
server_name mydomain;
ssl_certificate /etc/ssl/CA_Bundle.ca-bundle;
ssl_certificate_key /etc/ssl/2021/server.key;
location / {
add_header Access-Control-Allow-Origin *;
proxy_set_header Host $host;
proxy_pass http://172.17.0.1:8080;
proxy_redirect off;
expires off;
set $agentflag 0;
if ( $http_user_agent ~* "(Mobile)" ){
set $agentflag 1;
}
if ($request_uri ~ "user-agent"){
set $agentflag 0;
}
if ( $agentflag = 1 ) {
rewrite ^/(.*)/$ /$1 permanent;
return 307 https://mobile.mydomain$request_uri;
}
}
}
server {
listen 80;
server_name mobile.mydomain;
return 301 https://$server_name$request_uri;
}
include mime.types;
server {
listen 443 ssl;
server_name mobile.mydomain;
ssl_certificate /etc/ssl/CA_Bundle.ca-bundle;
ssl_certificate_key /etc/ssl/2021/server.key;
location / {
add_header Access-Control-Allow-Origin *;
proxy_set_header Host $host;
proxy_pass http://172.17.22.1:8081;
proxy_redirect off;
expires off;
}
}

Answer 1

It is working fine now,
I have used proxy_pass , instead of rewrite.
if ( $agentflag = 1 ) {
proxy_pass http://IP-address-mobile-app;