If a device has not been online for a period of time, the device will be flagged as “Lost” within the Honeywell system. If the device is in that state and a command is sent to the device, an immediate error will be generated in Events2HVAC:
“StatusCode [400] BadRequest - Error: [DeviceIsLost] - Device is lost.”
To correct this error, make sure your device is connected to WIFI and registered in the Honeywell portal.