Webpage card showing content of local web server only in browser but not in companion app

I have a local web server streaming the webcam of my 3D printer to a browser. The webpage is accessible on the local network as https://local IP, which I also use as a URL in the webpage card. It shows nicely on HA via Browser, but the card remains blank in the companion app. Any ideas?

In the companion app under Settings->Companion App->(the first choice, not sure what it is called) under “DETAILS” there is “Internal URL” and “External URL”, my “Internal URL” has the internal IP and port to HA. Note sure if that is it, but it’s an idea…

Thanks for the hint! I checked the setting; the app says it would be connected locally, but still does not show any content.