Old-fashioned hot shoe flash does not fire on my Lumix G7

I have a Lumix G7 camera, and a Hanimex TS755M external flash from a junk shop. When connected to the camera, it doesn’t fire.

• I have checked the Hanimex flash voltage, both looking it up on http://www.botzilla.com/photo/strobeVolts.html and measuring it myself — it should be safe. (It would be nice if the G7 manual actually listed the voltage limit.)

• The flash fires fine if I charge it and press the test button, so that bit works.

• The camera is detecting the presence of the flash, presumably using the READY pin on the hot shoe, so that bit works.

• If I short the central pin on the flash to the ground connector on the side, it doesn’t flash. Actually, testing this again, this works fine. Apparently I just wasn’t making decent contact before.

Is this pointing to a defunct flash, or is it more likely that there’s a configuration issue on the camera which I’ll need to fix before it’ll operate the external flash (which TBH seems unlikely given that it’s detected)? Alternatively, I haven’t been able to find a manual for the Hanimex flash, so maybe I’m doing something wrong there; but it only has two controls…

Edit 2: here’s a picture of the shoe in question. It’s at an angle to show the ground connector on the side (the shoe itself is plastic and non-conductive). The extra stud on the base appears to connect to the Nikon READY pin, but who knows what that pin is doing on a Panasonic/Lumix camera.

Edit 3: Following a suggestion in the comments below, I tried taping over the extra pin on the bottom of the shoe. This is harder than it looks as the pin is quite pointy, but it does appear that with it taped over, the camera is still detecting flash readiness and the flash still doesn’t fire. So, maybe the camera is using signalling on the centre pin to detect readiness?

Edit 4: I tried the flash on another camera (an old Canon EOS). It worked absolutely fine. So there’s nothing wrong with the flash.