Hello,
I am currently trying to register the application in the Developer Home.
As described, I enter “http://my.home-assistant.io/redirect/oauth” in the redirect ULR
I have also checked that the “http://my.home-assistant.io is redirected correctly.
However, when I try to save the application registration, I get the following error message in the Developer Home: ”The character / is not allowed.”
I would be grateful for any tips!
Best regards
Ralf
Sane here. All this procedure and api seems to be a little … crappy from Home-Connect side.
unaouthorized blablabla error, wasted one hour.
-custom domain over cloudflare.
-with/without default_config: doesnt matter.
-deleted “Application Credentials”
-added manual “Application Credentials” from the button.
Works like nothing happened.
This is the solution if you have already integrated home connect and have created a new app at https://developer.home-connect.com/. Then, of course, the credentials are no longer valid. 
I had an issue this evening with home connect where devices became unavailable. After some messing about with restarts and reloads I decided the best approach would be to delete the integration and re-install. Unfortunately, having done so, I was still getting client error messages when trying to connect to the api server for home connect.
I first set up the connection to home connect 18 months ago and, at the time, the suggestions and comments in this post helped get the integration working however, by the end of the evening I have found that either the prior issues have been corrected or the issue is no longer there, and the suggested work arounds did not work anymore.
Next step I took was to delete the app in my home connect developer tools account so that I have a clean start and to recreate a new one with new credentials. I use the url redirect I used in the past which was http://HA_ip_address/auth/external/callback
On trying to re-install I saw the process was using the old credentials so dug around to find and delete them. Having sorted that and set up new credentials I still had issues with client errors trying to authenticate with api.home-connect
In the end I went back to the base instructions in HA ( https://www.home-assistant.io/integrations/home_connect/ ), used the redirect they provided https://my.home-assistant.io/redirect/oauth, and it all worked.
The instructions also provided the link on how to find and delete the existing credentials which, had I have gone there first, would have helped save time.
So … that’s 4 hours I will not get back but have learned that sometimes its best to reset and go back to the start
I hope that by posting this I might save someone else time…
I would suggest you used the / in the Application ID * field … that should just be a name you give the application … eg “HomeAssistant”
They also had a server outage, which is partially still ongoing. There’s a ticket for this on github and a notification in the home connect app.
I can confirm that the Home Connect integration won’t load at this moment - and also the info by @markus.schloesser that the home connect app itself has a message about ongoing problems. App itself is also affected.
Home connect Integration is working again.
I had the same issues, with an invalid client ID and whatever described above I tried, no luck.
What fixed the problem for me, was to add the credentials from Home Connect, into Home Assistant, in the menu Settings → Devices & Services → Application Credentials (menu with three dots in the top right). This might be very obvious for some, but I didn’t know to put the credentials there. After that I started adding the Home Connect integration and then everything works like a charm.
For anyone who got stuck with setting this up. Follow up HA documentation, but do the HA configuration while opening HA in browser Private mode. Definitely there can be cookies stored which prevent correct configuration requests and fails with authentication otherwise.