nginx internal communication between DO apps

So I’m trying to use the Digital Ocean App Platform. I have a node app deployed with the following app.yaml config:

name: my-app

services:
- name: admin
  github:
    repo: my-repo/admin
    branch: main
    deploy_on_push: true
  build_command: npm run build
  run_command: npm run start
  internal_ports:
  - 3000

This app should now be served at /admin.

To achieve that I added a nginx deployment to proxy to the internal 3000 port:

server {
    listen 80;
    listen [::]:80;
    server_name xxx.ondigitalocean.app;

    location /admin/ {
        set $app1 http://admin:3000;
        proxy_pass $app1;
        proxy_set_header Host $host;
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    }
}

When accessing my deployed app at https://xxx.ondigitalocean.app/admin/ I’m seeing We encountered an error when trying to load your application and your page could not be served. Check the logs for your application in the App Platform dashboard.

Checking the logs reveals: *424 no resolver defined to resolve admin

I can’t find anything on how to debug internal routing of the app platform and it seems like it’s related to that so I highly appreciate every sort of hint on this!