When I attempt to authorize the API client to communicate with Honeywell by going to https://udi-honeywellhome-auth.azurewebsites.net , entering my Client Id and Secret, I receive the prompt to log in to Honeywell Home. When I enter my credentials, I get a message stating "Please use an account with one or more devices installed." The Honeywell Home credentials I am using are the ones I use for the newest Honeywell Home app on my phone. That app is the First Alert app, and that app shows two thermostats present. If anyone else has encountered this, and found a workaround for it, please reply.

It may be the case that only accounts using the Honeywell Home app are supported, and not those using the First Alert app? The Honeywell Home app is still available, although supposedly it will eventually be replaced by the First Alert app.

Update: I tried to revert to Resideo Smart Home app (from First Alert app). This was not successful. One of my Honeywell thermostats would not register with the Resideo Smart Home app, and resideo tech support directed me to use First Alert app instead of Resideo Smart Home (since they are migrating everyone - new installs and anyone who calls with a problem). After I got both my thermostats working with the First Alert app, I tried again to authorize the API client. When prompted for the resideo credentials, I used my First Alert credentials, and I am getting a "username or password is incorrect" message. So since the Honeywell node server is no longer being maintained, it looks like things are not going to work with the First Alert app.

For the benefit of anyone trying to use a Honeywell thermostat, I can confirm if you use the zwave version instead of the wifi version you will be able to natively add the thermostat to IoX. (I purchased a home that has the wifi versions, but I have used zwave versions in past houses with no issues.)

Edited June 30Jun 30 by wmcneil
fix typo