Websocket insecure not allowed - why if the webserver is on LAN and is proxied by NGINX?

[dcaccount]

Hello,
I have a Raspberry Pi4 with Lighttpd web server and Node-RED.

I have created a simple web site with a web socket connection in JavaScript between Lighttpd and Node-RED to get some energy data and display them on the website. On the LAN everything works perfectly.

I have then installed NGINX Proxy Manager to work as reverse proxy for the web server.

I would in fact like to connect with SSL to the reverse proxy, keeping unsecured the communication between the webserver Lighttpd and Node-RED, being on the LAN.

In NGINX I have created a new host, forwarding the hostname (casa.example.org) to the LAN IP address of Lighttpd (192.168.99.199) and port 80.

The problem is that the browser refuses to open the web socket connection and the error that I get from Safari is:

The page at https://casa.example.org was not allowed to run insecure content from ws://192.168.99.199:1880/ws/energy.

As said, 192.168.99.199 is the address of the Raspberry where the webserver, the NGINX reverse proxy and Node-RED are installed.

Can anyone please help me understand where I am wrong?

Thanks,
Daniele