Can't Install Smart Things Integration

I am new to HASS, but have a stable Smart Things environment, all ZWave. I want to do a test drive of HASS.

I have signed up for the 1 month free Nabu Casa trial and can access my home via PC browser locally (homeassistant.local:8123) and remotely (xxx.ui.nabu.casa/lovelace/0). I can view remotely with the Android app.

When I try to add the Smart Things integration, I get a popup windows that says “Error Config flow could not be loaded: undefined”. I never got the chance to enter my access secret.

These threads imply there is an issue with the external URL:

However, my URL is configured. I can remotely access my home via Android when WiFi is off, and the nabu.casa domain in a PC browser gets me to the right place as well.

Log entry is:
Error handling request 3:35:00 PM – (ERROR) components/webhook/init.py

Where is init.py? I installed Studio Code Server and it is not in the file tree, there are only .yaml files

Any hints as to where to look?

Beuller?

More log info, where is the handler already defined?:
File “/usr/src/homeassistant/homeassistant/components/smartthings/smartapp.py”, line 226, in setup_smartapp_endpoint
webhook.async_register(
File “/usr/src/homeassistant/homeassistant/components/webhook/init.py”, line 46, in async_register
raise ValueError(“Handler is already defined!”)
ValueError: Handler is already defined!