Reverse Proxy NGINX and external Flask server

I am trying to mount a reverse proxy with nginx in an instance that only deals with proxy as a function of the route, and the servers are in other instances, this is the configuration:

server {
    # SSL configuration
    #
    listen 443 ssl default_server;
    listen [::]:443 ssl default_server;

    ssl_certificate /etc/nginx/ssl/ssl.crt;
    ssl_certificate_key /etc/nginx/ssl/ssl.key;
    server_name _;
    location /app1/{
            rewrite ^/app1(.*) /$1 break;
            auth_basic "Restricted"; #For Basic Auth
            auth_basic_user_file /etc/nginx/.htpasswd;
            proxy_pass http://<IP-SERVER1:PORT;
    }
    location /app2/{
            rewrite ^/app2(.*) /$1 break;
            proxy_pass http://<IP-SERVER2:PORT;
            auth_basic "Restricted"; #For Basic Auth
            auth_basic_user_file /etc/nginx/.htpasswd;
}

So far, well, because the requests arrive at the server in particular, in one of the servers I hope to receive the request in / and make the request to the local server flask, the problem comes when flask treats the routes, theoretically it should be link But use: link >  and arrives at the reverse proxy and gives 404. The configuration of app2:

server{
    listen 8787 default_server;
    listen [::]:8787 default_server;
        server_name _;

    location / {
           proxy_pass http://127.0.0.1:7000/;
           proxy_set_header Host $host;
           proxy_set_header X-Real-IP $remote_addr;
           proxy_set_header X-Forwared-For $proxy_add_x_forwarded_for;

            }
}

Thank you very much !!