This was harder than it should be. The process that finally worked was something like this:
- Disable cellular data on iPhone
- Forget wireless network on iPhone
- Press the Menu button on thermostat, press Mate twice, ensure yellow light is flashing
- Connect to thermostat wifi network on iPhone
- Go to http://192.168.10.1/ in browser on iPhone
- Follow the 5 steps and enter requested details: wifi network, wifi password, provisioning code
- If you're lucky, the thermostat chirps and then green light flashes
It seemed like the iPhone had trouble staying on the thermostats network and the provisioning process kept timing out.
I had a lot of trouble getting the browser to connect, for more details, see this
FAQ: