Nginx get 404 when accessing PHP files but the server works fine

I am struggling to get nginx processing *.php files in a container app. I have read all over the places, even here in SO, but everything I have tried still not working for me meaning I am able to access the web server through http://localhost:8080 but if I do http://localhost:8080/index.php I get a 404. I have check the path /app/src on both containers: php-fpm and nginx and it has a index.php file which contains just: <?php phpinfo(); ?>.

I am building the nginx container using the following Dockerfile:

#syntax=docker/dockerfile:1.4

FROM nginx:alpine-slim

COPY --link ../nginx/conf.d/nginx-dev.conf /etc/nginx/conf.d/
COPY --link ../nginx/conf.d/php-upstream.conf /etc/nginx/conf.d/

and the content of each of those files is as follow:

# nginx-dev.conf
server {
    listen 80 default_server;
    listen [::]:80 default_server;
    server_name app.localhost localhost;
    root /srv/app;

    location / {
        # try to serve file directly, fallback to index.php
        try_files $uri @rewriteapp;
    }

    location @rewriteapp {
        rewrite ^(.*)$ /index.php/\ last;
    }

    location ~* .php(/|$) {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        fastcgi_pass php-upstream;
        fastcgi_split_path_info ^(.+.php)(/.*)$;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_param HTTPS off;
    }

    # Serve PHP-FPM status page, note that we should not activate this in production
    location ~ ^/status$ {
        access_log off;
        include fastcgi_params;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        fastcgi_pass php-upstream;
    }

    gzip on;
    gzip_disable "msie6";
    gzip_vary on;
    gzip_proxied any;
    gzip_comp_level 6;
    gzip_buffers 16 8k;
    gzip_http_version 1.1;
    gzip_min_length 1024;
    gzip_types text/plain text/css application/json application/javascript application/x-javascript text/xml application/xml application/xml+rss text/javascript application/vnd.ms-fontobject application/x-font-ttf font/opentype image/svg+xml image/x-icon;
    gzip_static on;

    server_tokens off;
    disable_symlinks off;
    fastcgi_buffer_size 256k;
    fastcgi_buffers 4 512k;
    fastcgi_busy_buffers_size 512k;

    error_log /var/log/nginx/app_error.log;
    access_log /var/log/nginx/app_access.log combined buffer=64k flush=5m;
}

# php-upstream.conf
upstream php-upstream {
    server php-fpm:9000;
}

last but not least, this is the PHP-FPM configuration that goes inside the php-fpm container:

[global]
daemonize = no
process_control_timeout = 20

[www]
listen = /var/run/php/php-fpm.sock
clear_env = no
listen.mode = 0666

Can any see something that I am not? Where is the problem here?