Just had to play with it a little to test it out. FWIW, you have to go back and add Hubitat to the allowed Redirect URI's in order for the authorization to work from the app.
The specific site URI you need is: https://cloud.hubitat.com/oauth/stateredirect
Add Authorized URI
Before I did that, I was getting a 400 error. Afterwards, it discovered my devices.
Another quirk, I had to click done after entering the Project ID and Json. Then I was able to come back into the app and click authorize. So, it was not showing the authorize button until after I clicked done (even though I had filled out the fields. I tried to tab out and clicking on white space. Neither worked)
