It should work, but I can’t test it myself. I have received successful reports but that was from people that were already using the app, and thus already had installed their thermostats.
If the screen is white after ‘follow the instructions’, that means that it cannot find any thermostats for some reason. The most common fault is username and password errors, but I assume you did check that
Can you restart the app, try to add devices and then submit an app diagnostics reports? This is done via Settings / Apps .