I have the same, or similar, issue. I had to install the Nest thermostat through the Google Home app, but when I tried to install the sensor, it said I had to do this through the Nest app. So when I try to install the sensor through the nest app, it says I have to have a thermostat installed in the Nest app. When I try again to install the thermostat through the Nest app, it again says it needs to be installed through the home app. Can you please provide a solution to this issue? Thanks
I had the same issue. I clicked on my account pic in the Nest app and logged out. When I logged the Nest app back in, there was an "+ Add a Product" option under settings. Scanned the QR code and it worked. Wait a few minutes after setting up for the option to show up in the Nest app as an alternate place to set a temp. Also visit the Settings to set when the system should use the Temp Monitor vs Thermostat. Hope this helps.
I've yet to get the Nest App to show the temp at the Remote Sensor but that may show up with time.