HT-M01S local pi-zero mosquitto

Hi all.
Getting an error screen “Disconnect from server, please check network.”

I am able to connect to TTN and send/receive data from a Cube Cell LoRa device through a HT-M01S gateway (firmware 1.4), so the hardware appears to be working correctly.

Is it possible to connect HT-M01S with a local gateway (Raspberry Pi Zero with Mosquitto)?
Mosquitto is running on a Pi-Zero which is connected to local network through WiFi.
The IP of Pi-Zero is 192.168.0.27 on port 1883.
HT-M01S config SERVER ADDR = “192.168.0.27” and SERVER PORT = “1883”.
I have tried configuring the HT-M01S using both WiFi and Ethernet - both appear to connect, but after about 20 seconds show “Disconnect from server, please check network” on the display.

Cheers - BillT