Edit: well, this is embarrassing, but I replaced this TRV with another nearer to my dongle in a clear line without obstructions and it is identified as “TS0601
by _TZE204_vjpaih9f”, so it’s working. Please disregard the rest. Maybe my batteries not up to the task or something 
I bought a supposedly AVATTO branded TRV, although the packaging didn’t reveal this. It’s an N-TRV16 by it’s label.
I have a Sonoff Zigbee 3.0 USB Dongle Plus V2 (bought from here) this actually has the Sonoff brand on it, the device and the package.
I have the latest HAOS running.
The dongle is picked up via the Zigbee Home Automation integration.
But I cannot add my TRV.
I’m turning the TRV down to 5 celius and below to turn it “OF” and then pressing the button on it for a few secs, then it lights up and I can see the “network” icon flashing, but (Z)HA cannot find it.
The Sonoff dongle and the TRV is apart like 10 meters on the same floor inside the house.
Also tried MQTT, but that didn’t do the trick either.
Any ideas? What to try? Where to go?