Cant access sub paths on Nginx + React router behind a proxy - reactjs

Question

I have an nginx server with a local web app running locally in port 4000. I was able to create the Nginx rules to have it loaded trough the proxy, but now I can only access the website trough the main url, like "https://app.domain.com" (this works well), if I try entering trough any link like "https://app.domain.com/page" I get a 404.
This is my current nginx config;
server {
# gzip
gzip on;
gzip_vary on;
gzip_proxied any;
gzip_comp_level 6;
gzip_types text/plain text/css text/xml application/json application/javascript application/xml+rss application/atom+xml image/svg+xml;
# SSL configuration
listen 443;
listen [::]:443;
expires $expires;
ssl on;
ssl_certificate /etc/ssl/app.crt;
ssl_certificate_key /etc/ssl/app.key;
index index.html;
server_name app.domain.com;
proxy_intercept_errors on;
autoindex off;
root /var/www/domain-app;
# I am using this rule to allow files like icons or css to be accessed directly
location ~ ^.+\..+$ {
proxy_set_header Host $host;
proxy_pass http://localhost:4000;
proxy_redirect off;
if (!-e $request_filename){
rewrite https://$server_name break;
}
try_files $uri /index.html;
}
location / {
proxy_set_header Host $host;
proxy_pass http://localhost:4000;
proxy_redirect off;
try_files $uri /index.html;
}
}
I tried something like this on the location and it worked for root domain and for pages, but accessing the site from a sub-page like "https://app.domain.com/page/sub" failed; It loaded the page but it tried to find the assets under "https://app.domain.com/page/static/..."
location / {
proxy_set_header Host $host;
proxy_pass http://localhost:3000;
proxy_redirect off;
set $fallback_file /index.html;
if ($http_accept !~ text/html) {
set $fallback_file /null;
}
try_files $uri $fallback_file;
}

Answer 1

Alright, for anyone coming here I found the solution after some hours of research;
The problem was not my nginx config after all, but rather a Create React App/react-router thing.
In order for the URI of the assets to be properly replaced in all sub-paths by the application (NOT the server) your homepage in package.json needs to match the URL of your internal server/Proxy, so for example I was hosting the proxy locally at "http://localhost:4000" then that should also be the "homepage" attribute in package.json, differently from what other tutorials suggest of using just "./", since this is not a single page app.
Chhers!