Can't Create Reverse Proxy from Droplet to App Platform

I am unable to setup a reverse proxy from my nginx docker container in a droplet to the URL generated from the App platform.

I’m able to ping https://foo-bar-doo24.ondigitalocean.app/ from the browser, from the droplet and inside the container using bin/sh but when I test the proxy I see these errors in the log file: #20: *4 connect() to [###:####:##::##]:443 failed (101: Network unreachable) while connecting to upstream - 403 error #20: *4 upstream server temporarily disabled while connecting to upstream, - 421 error

And on the client side I’m receiving a CORS error: https://foo.com/' from origin 'https://foo.com' has been blocked by CORS policy: Response to preflight request doesn't pass access control check: No 'Access-Control-Allow-Origin' header is present on the requested resource. If an opaque response serves your needs, set the request's mode to 'no-cors' to fetch the resource with CORS disabled.

This is what my nginx config file looks like:

server {
  listen 443 ssl;
  http2 on;

  server_name foo.com;

  ssl_certificate /etc/ssl/cert.pem;
  ssl_certificate_key /etc/ssl/key.pem;
  ssl_client_certificate /etc/ssl/ssl.crt;
  ssl_verify_client on;

  ssl_buffer_size 8k;
  ssl_protocols TLSv1.2 TLSv1.3;
  ssl_prefer_server_ciphers on;

  location / {
    proxy_pass https://foo-bar-doo24.ondigitalocean.app/;
    proxy_set_header Host $host;
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-Host $host;
    proxy_set_header X-Forwarded-Proto https;

    proxy_buffer_size 16k;
    proxy_buffers 4 32k;
    proxy_busy_buffers_size 64k;

    proxy_connect_timeout 60s;
    proxy_send_timeout 60s;
    proxy_read_timeout 60s;
    send_timeout 60s;
  }
}

If anyone could shed some light on what I’m doing wrong it would be immensely helpful! Thank you!