Pri ter connects but doesn't respond to Octoprint t

Hi, I have installed Octo4a on a Galxy S9, so reasonably powerful and running Android 12.

The Octo4a app shows server running, camera server running, but printer not connected.
When I connect the printer (using a known good OTG cable through which I can successfully connect to storage devices, for example) the printer makes a slow, gentle grinding sound but does nothing.
It will not respond to, for example, Home commands from the Octoprint interface and it does not respond to any commands from the terminal (G1, G28, M503 for example).

It does not echo the command or act on it.

Clicking Disconnect is ignored and the printer remains connected.

Any ideas?
Many thanks