How to host a react app in custom route using Nginx? - reactjs

Question

I'm trying to host express API in the root route(/) and react app in the app route(/app). If I go to https://<domain> then I can access the express app but if I go to https://<domain>/app then I can't access the react app. It says:
403 Forbidden
nginx/1.14.0 (Ubuntu)
Here is the config file for Nginx:
server {
server_name <domain>;
location /app/ {
root /var/www/html;
index index.html index.htm;
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;
try_files $uri $uri/ /index.html;
}
location / {
proxy_pass https://<ip>:<port>;
proxy_http_version 1.1;
proxy_set_header Upgrade $http_upgrade;
proxy_set_header Connection 'upgrade';
proxy_set_header Host $host;
proxy_cache_bypass $http_upgrade;
}
listen 443 ssl; # managed by Certbot
ssl_certificate /etc/letsencrypt/live/<domain>/fullchain.pem; # managed by Certbot
ssl_certificate_key /etc/letsencrypt/live/<domain>/privkey.pem; # managed by Certbot
include /etc/letsencrypt/options-ssl-nginx.conf; # managed by Certbot
ssl_dhparam /etc/letsencrypt/ssl-dhparams.pem; # managed by Certbot
}
server {
if ($host = <domain>) {
return 301 https://$host$request_uri;
} # managed by Certbot
listen 80;
server_name <domain>;
return 404; # managed by Certbot
}