App not accepting key code

[Mazza1]

I am new to a home with Nest, I have reset all settings but my app is not accepting the key code given on the device despite trying this many times 

[David_K]

First check which model of thermostat you have:
How to tell which Nest thermostat you have - Google Nest Help

Nest Thermostat (2020), Nest Learning Thermostat (4th gen)

1. On the thermostat, go to Settings > Account > Disconnect.
2. Follow the setup steps: Get started with your Nest Thermostat - Google Nest Help

Setup these models using the Google Home app. The QR code and setup key are physically printed on the back of the thermostat for Nest Thermostat (2020) and will be displayed on screen for Nest Learning Thermostat (4th gen).

Nest Thermostat E, Nest Learning Thermostat (1st, 2nd, 3rd gen)

1. On the thermostat, go to Settings > Reset > Account connection. If you don't see this option, you'll need to select All settings.
2. Follow the setup steps: Add your Nest thermostat to the Nest app - Google Nest Help

Setup these models using the Nest app. The QR code and setup key are in the settings on the thermostat itself and are not printed on the device.