Smarthings cannot be connected


I have a problem connecting my Samsung AC via Smarthings to home assistant.
Following Setup:
HA ist installed on a virtual instance on my synology nas and via reverse proxy accessible via intranet (this works fine). SSL-Certificate from Let’s encrypt via the NAS.
When I try to setup the smartthings integration I always receive the error message: [SmartThings could not validate the webhook URL for Home Assistant].
When I try to open the webhook URL I receive an Error 405.

In one forum there was a hint, that the Certificate is not valid. For the browser it is, but, when I use a SSL Checker and check my domain, I get the message: Unable to connect to the server

I assume, that this is the reason, why the smartthings fails.
Therefore my questions:

  • Does nayone know, if this is really the problem
  • How can I fix it (Certificate issue)
  • Do I need the install a separate webhook add-on?

Thanks in advance for your help.

If this is true it is 100% the issue. If you cannot validate the cert, you cannot secure the comms tunnel and therefore no connection.

As to how you fix it. That depends on HOW it’s broken. Gotta see what your tool said.

I solved it with Nabu Casa. Thanks!