Diagnosis
The thermostat is on your local network but can't reach Emerson's servers. This is usually a router firewall or band issue.
How to Fix It
Reboot your router and modem. Power cycle the thermostat by pulling it off the wall plate for 30 seconds. Reconnect. On your phone, disconnect from mobile data and use only home Wi-Fi. Try the setup again in the Sensi app.
If That Didn't Work
Your router may be blocking the connection. Temporarily disable any advanced firewall settings like AP Isolation or Client Isolation. Ensure the thermostat is on the 2.4 GHz band. The Sensi Lite does not support 5 GHz networks.
Heads Up
The thermostat must be within a strong signal range of your router. Thick walls or distance can cause a weak signal that passes setup but fails to maintain a cloud connection.