Hi! I understand you're encountering a registration error with your tado° smart room thermostat on your Android device. To help you better, could you please tell me a bit more about the exact error message you see? Also, have you tried registering the thermostat before on a different account or device?

Meanwhile, here's a general step-by-step approach to address common registration errors with tado° thermostats on Android:

1. Check if the thermostat is already registered: Sometimes the device might be linked to another tado° Home or account. If so, the app will decline registration. You can verify this by:
- Logging into your tado° account on the web or app and checking your Homes and Devices.
- If the thermostat is linked elsewhere, remove it from that account before trying again.

2. Clear app cache and restart the app:
- On your Android device, go to Settings > Apps > tado° > Storage > Clear Cache.
- Close and reopen the app to retry registration.

3. Ensure correct account credentials:
- Double-check that you’re logged into the right tado° account that should own the thermostat.

4. Activate pairing mode on the Internet Bridge (if applicable):
- Open the tado° app > Settings > Rooms & Devices.
- Select the Internet Bridge and choose “Activate pairing”.
- Then, try adding the thermostat again.

5. Restart devices:
- Power off the thermostat and the Internet Bridge (if you have one).
- Restart your Android phone.
- Turn everything back on and attempt registration anew.

If these steps don’t resolve it, there could be more advanced causes like server-side issues or firmware mismatches. In that case, we might try specific account/device checks or perform a factory reset on the thermostat.

Let me know what you’ve tried so far and the error message details, so I can guide you further!

Meanwhile, here’s a support link with related scenarios that might help:
https://support.tado.com/en/articles/3487612-when-installing-tado-the-app-says-that-my-device-is-already-registered-how-can-i-fix-this [3]

Are you satisfied with this initial guidance?