Enviro for Raspberry Pi: Gas sensor not connected

I have just purchased a Enviro for Raspberry Pi, and attached it to a raspberry pi zero 1 w, and when running the gas.py command I got:
~/enviroplus-python/examples $ python gas.py
2023-02-18 17:00:11.863 INFO gas.py - Print readings from the MICS6814 Gas sensor.

Press Ctrl+C to exit!

Traceback (most recent call last):
File “/home/pi/enviroplus-python/examples/gas.py”, line 20, in
readings = gas.read_all()
File “/usr/local/lib/python3.9/dist-packages/enviroplus/gas.py”, line 98, in read_all
raise RuntimeError(“Gas sensor not connected.”)
RuntimeError: Gas sensor not connected.

The temperature, humidty etc do give measurements and they are sensible. I soldered the connectors onto the raspberry pi zero 1 w myself (and so could have made a mistake there). The pins look ok, but what pins should I look closely at. Could it be a flaw in the raspberry pi zero, the enviro, or is it my soldering?

Thanks in advance for any help.

Enviro or Enviro + ?
The + has the gas senser.

OOps, I didn’t realise there were two version, I got the PIM486 version which is the enviro one I think. So it looks like the sensor is indeed not connected!

Yeah, there was the Enviro, and then the + version with some extra features.
Adding this should get you that functionality if you wanted it.
MICS6814 3-in-1 Gas Sensor Breakout (CO, NO2, NH3) (pimoroni.com)