For those who find this thread, the answer was to pair the g6 with the ttlock app first. Hitting the + button then selecting the g6 allowed me to add my wifi credentials to the device and get it on the network.
If you then power off the device, everytime its powered on, you get about a minute to re-pair it before it re-joins the network, and this is enough to then pair it with HA.
TDLR:- Dont bother, the matter support for the g6 is poor and flakey. See this thread for more details, starting about here:-