Invalid Panel URL (Apache on Port 8080)

I am currently trying to run both a Nuxt.js frontend app and Kirby as a backend app on the same Digital Ocean droplet. To achieve this I am using Nginx to serve the app on localhost:8000 and proxy all requests to url.com/cms to localhost:8080.

I’ve set up Apache to run on port 8080. I’ve also set up a virtualhost for url.com and ran a2ensite to connect it.
The actual kirby installation works. I can also fetch my custom api via /api/data, only the panel throws an error.

Does anyone have any idea why? I can’t seem to figure it out. I’ve tried reinstalling the panel as well with no success.

Here is my config:

/etc/nginx/sites-enabled/default

# HTTP — redirect all traffic to HTTPS
server {
    listen 80;
    listen [::]:80 default_server ipv6only=on;
    return 301 https://$host$request_uri;
}

# HTTPS — url.com -> STJB_Frontend
# HTTPS - url.com -> Apache:8080 -> STJB_Backend
server {
    # Enable HTTP/2
    listen 443 ssl http2;
    listen [::]:443 ssl http2;
    server_name url.com;

    # Use the Let’s Encrypt certificates
    ssl_certificate /etc/letsencrypt/live/url.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/url.com/privkey.pem;

    # Include the SSL configuration from cipherli.st
    include snippets/ssl-params.conf;

    location /cms  {
        proxy_set_header Host $host;
        proxy_set_header X-Forwarded-For $remote_addr;
        proxy_pass http://localhost:8080/;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-Forwarded-Proto $scheme;
    }

    location / {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header X-NginX-Proxy true;
        proxy_pass http://localhost:8000/;
        proxy_ssl_session_reuse off;
        proxy_set_header Host $http_host;
        proxy_cache_bypass $http_upgrade;
        proxy_redirect off;
    }
}

/etc/apache2/sites-available/studiojohannesbissinger.com.conf

<VirtualHost *:8080>
    ServerName studiojohannesbissinger.com
    ServerAlias www.studiojohannesbissinger.com
    DocumentRoot /home/studioscholz/apps/STJB_Backend
    <Directory /home/studioscholz/apps/STJB_Backend>
        Options Indexes FollowSymLinks MultiViews
        AllowOverride All
    </Directory>
</VirtualHost>

And here is the Error Log:

Kirby
Kirby Toolkit	v2.5.10
Kirby CMS	v2.5.10
Kirby Panel	v2.5.10
GET Data empty
POST Data empty
Files empty
Cookies
kirby_session	tphnpl6taekejr91s7n614cii4
Session
kirby_session_fingerprint	e8c4171aa1a81f0896751833c1626d1a31fb51f2
kirby_session_activity	1528873385
Server/Request Data
USER	www-data
HOME	/var/www
PATH_TRANSLATED	/home/studioscholz/apps/STJB_Backend/panel/index.php
PATH_INFO	/panel/index.php
SCRIPT_NAME	/php-fcgi
REQUEST_URI	//panel/
QUERY_STRING	
REQUEST_METHOD	GET
SERVER_PROTOCOL	HTTP/1.0
GATEWAY_INTERFACE	CGI/1.1
REDIRECT_URL	/panel/index.php
REMOTE_PORT	59854
SCRIPT_FILENAME	/usr/lib/cgi-bin/php-fcgi
SERVER_ADMIN	[no address given]
CONTEXT_DOCUMENT_ROOT	/usr/lib/cgi-bin/php-fcgi
CONTEXT_PREFIX	/php-fcgi
REQUEST_SCHEME	http
DOCUMENT_ROOT	/home/studioscholz/apps/STJB_Backend
REMOTE_ADDR	127.0.0.1
SERVER_PORT	80
SERVER_ADDR	127.0.0.1
SERVER_NAME	url.com
SERVER_SOFTWARE	Apache/2.4.18 (Ubuntu)
SERVER_SIGNATURE	<address>Apache/2.4.18 (Ubuntu) Server at url.com Port 80</address>
PATH	/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
HTTP_COOKIE	kirby_session=tphnpl6taekejr91s7n614cii4
HTTP_ACCEPT_LANGUAGE	de-DE,de;q=0.9,en-US;q=0.8,en;q=0.7,la;q=0.6
HTTP_ACCEPT_ENCODING	gzip, deflate, br
HTTP_ACCEPT	text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8
HTTP_USER_AGENT	Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_4) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/66.0.3359.181 Safari/537.36
HTTP_UPGRADE_INSECURE_REQUESTS	1
HTTP_CACHE_CONTROL	max-age=0
HTTP_CONNECTION	close
HTTP_X_FORWARDED_FOR	109.125.116.104
HTTP_HOST	url.com
REDIRECT_STATUS	200
REDIRECT_HANDLER	application/x-httpd-fastphp
FCGI_ROLE	RESPONDER
PHP_SELF	/panel/index.php
REQUEST_TIME_FLOAT	1528873385.0487
REQUEST_TIME	1528873385
Environment Variables empty
Registered Handlers
0. Whoops\Handler\PrettyPageHandler