@Kruemelmonster Even after enabling third-party compatibility, is the P110 still unable to be controlled via HA?

  @xwc Yes, since updating to firmware version 1.4.2, it has not been possible to authenticate in Home Assistant, even after disabling and re-enabling third-party compatibility in the Tapo app.

Authentifizierung nicht möglich: Unable to complete handshake: 192.168.X.X: TRANSPORT_UNKNOWN_CREDENTIALS_ERROR(1003) (error_code=TRANSPORT_UNKNOWN_CREDENTIALS_ERROR)

It is the Tapo P100M in my case.

  @Kruemelmonster I recommend removing the P100M from Tapo (or pressing and holding the switch button for at least 10 seconds—it must be at least 10 seconds), then reconfiguring the P100M. After configuring the P100M, enable "Third-Party Compatibility" in Tapo.

The P100M supports Matter, so if you have speakers from Apple, Alexa, Google, SmartThings, or other platforms, here’s another method you can try:
1. Configure the P100M in Tapo.
2. In Home Assistant (HA), click "Add Device," select "Matter," and then choose "Devices in Use."
3. Next, select your Apple or Alexa or Google device and scan the Matter code on the P100M.
4. Once added successfully, you can use the P100M in Home Assistant.
Give these steps a try—hope this helps!

Same issue for me. I purchased 2x from Amazon a couple of weeks ago, and one of them is working in Home Assistant (via TP-Link Smart Home integration) and the other one isn't working with authentication failures. Matter works fine for both.

I of course have the Enable 3rd party apps turned on. I've tried turning it off and then back on and resetting the device and setting it up again, but no joy.

Home Assistant DOES automatically detect the device, but can't add it due to the authentication issue. 

  @xwc Thank you. However, I also have smart Tapo plugs without Matter support, for which I have currently (and luckily just in time) disabled automatic firmware updates. For the sake of clarity, I would prefer to have all of them available within the same TP-Link integration in Home Assistant.

Unfortunately, removing, resetting, and re-adding the Tapo plugs does not resolve the issue. This is very obviously a problem tied to the recent firmware versions.

This issue is also being reported elsewhere, here are a few examples:

• https://github.com/python-kasa/python-kasa/issues/1653

• https://community.tp-link.com/en/smart-home/forum/topic/863296?moduleId=614