Port forwarding for Duo streaming on the internet to Android

Hi

I am fairly proficient in IT generally, having worked in support for almost 30 years, but I have an issue that is giving me some problems.

I have forwarded port 80 on my router / Duo, and subsequently can stream via HTTP on pc's outside of my network without issue.

The problem comes when using ES File Explorer on my phone / tablet.

ES just won't even display a file list, let along stream. ES will do all of this ok within my network.

So, as an experiment, I temporarily put the duo into the DMZ - problem resolved, but security wise - not a great idea!

I think this proves beyond reasonable doubt that a port needs to be forwarded - but which one is the question :shock:

I have tried 8080 and 8200 - but no joy.

Any suggestions please, my fellow NAS-ers?

Thanks in advance......