Self hosted - Docker Container access to Host

Hi, need some help.

My self hosted retool server (Ubuntu) is hosting an API (Gunucorn Flask App) locally on the host. Using Nginx I'm attempting to use the configured URL on HTTPS 443 to proxy_pass to the app on the host. (Side note if i POST directly to the host IP the servic woeks 100%, but I need to move this to HTTPS thus the requirement - http://publicip:5000/receiver/receiver_app1


location /receiver {
    proxy_redirect off;
    proxy_set_header Host $host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;

My challenge is that I'm simply not getting the Nginx docker container for retool to see the host network or application on port 5000 to pass on these POST transactions.

I've tried numerous bridge networks including an attempt to connect nginx to the predefined host network, however the startup then fails as it states host network isn't defined in docker-compose.yml. You also can't specify a network as driver:host as there can only be one and that's the predefined host network.

Some assistance would be appreciated.