Home Connect integration - not working any more?

I am trying to get this integration working as well, but I’m still getting

  "error": "unauthorized_client",
  "error_description": "request rejected by client authorization authority (developer portal)"

despite numerous attempts and complete resets.

I have an app in developer.home-connect that has:

Application ID: HA
OAuth flow: Authorization Code Grant Flow
Redirect URI: Link to OAuth2 Authorize Callback – My Home Assistant (which I have set correctly, both using my external URL and using my internal URL)

Which gives me a client ID and client secret.

I then go to HA (where I have removed any old integration credentials) and add a New integration > Home Connect:

Name: HA
Client ID: the client ID
Oauth secret: the client secret

And again, I get the same error. Restarted HA several times in between resets, nothing helped.
Someone mentioned deleting something in the YML files but I can’t find anything related to home-connect in any of my YML files…

Also tried to “old” redirect URL that I found in another topic, despite the fact that the docs clearly state that tne new url (redirect/oauth) is the right one, but that also doesn’t work (yet this person says it does work with that “old” URL, posted 25 days ago).

Does anyone have a solution?