enable debugging https://github.com/Ludy87/ecotrend-ista#debug
Go to https://ecotrend.ista.de/ and log in. After that, click on the menu, select "Benutzerkonto" and scroll down to "Zwei-Stufen-Authentifizierung" then click on "Hinzufügen"
In step 2, the key will be displayed, which needs to be copied (it's best to write it down, as it will be required twice)
https://www.home-assistant.io/integrations/otp#configuration
# Example configuration.yaml entry
sensor:
- platform: otp
token: KEY_FROM_ECOTREND