I am trying to send commands from a Mac to a digital audio switcher that connects via USB and appears as a virtual serial/COM port.
I've installed CoolTerm, and it detects the switcher and can connect. But once connected, I can't type anything into the main console window of CoolTerm. I can select "send string" and type text into that small pop-up window, but when I do that I get no response from the device.
The device has a documented series of commands for checking the firmware, changing settings, and so on - so it has known-working serial functionality.
I don't know if this is relevant, but when I connect to the switch when no music/signal is playing through it, it sends an endless stream of status/error messages:

When I connect to the switch while music/signal is playing through it, the main CoolTerm console window is blank - the device is sending nothing to it.
But in either situation, I cannot type anything myself into the CoolTerm console window. And I cannot get any response whatsoever if I use the "send string" popup instead.
I've also tried connecting to another port (whatever comes up, for example Bluetooth), just to make sure it's nothing to do with this particular audio switcher, and still I cannot type anything into the main CoolTerm console then either.
Whenever I type a key, the virtual TX green indicator light does turn on momentarily in the bottom right of the CoolTerm window - but no text appears in the console and the cursor does not move.
To be clear, this is not about being unable to send any commands - I'm not even at that stage yet. I can't even type a command.
Hopefully I'm just being an idiot and missing something obvious. Thanks!