I use DuckDNS also. The “Sorry I could not reach” issue has been around for years, it comes and goes on its own. There isnt anything you have to do other than wait and it always sorts itself out after 2-60 minutes approximately. This issue, in the last couple months, has become more common. I’ll try using the re-sync tip to speed up the recovery. It would be nice to drop the google assistant and switch to local processing, but maybe this wont ever be possible because my speakers are all google.
I have duckdns setup with a single URL, mydomain.duckdns
I have my own domain setup in google domains with different dns entries for each app (home assistant, sonarr, emby, etc). home.mydomain, emby.mydomain, etc. I’m using nginx to forward those urls to the internal ip:port#. This all has always worked fine for me.
So i can access home assistant outside of my network by just going to home.mydomain.com. i dont include any port numbers or anything like I do internally.
One things I am getting confused on is the correct urls I should be using in the setup on the google side in the console cloud and console actions. In the walkthroughs I’ve watched it asks for you to use things like:
https://mydomain.com:8123/api/google_assistant
https://mydomain.com:8123/auth/authorize
https://mydomain.com:8123/auth/token
Do I need to use the port number in the URL since I dont need it when accessing HA externally?
Also, when I go to my HA internally or externally , it loads and adds /lovelace/dashboard to the end of the URL. Does /lovelace/dashboard need to be in the URL of the google setup?
Last question, in HA setup under Settings ->System->Network, for Home Assistant URL, do I need to put anything in there since I can access it externally as is?
Should the duckdns url be in there (like it shows in the UI example) or my google domains url?
For anyone that happens to have the same mistake as me. Verify you did not rename your file to “SERVICE_ACCOUNT.json” ; it needs to be “SERVICE_ACCOUNT.JSON” with the extension also capitalized.
Hello
that is really the solution. I’ve been at this for so long.
Many thanks from Germany to user beloved Spain 
How did you fix it? I’m having the same problem
For me, the login into my HA works and then, after a while, the message comes: “Could not reach [test] myapp. please try again.”
I suspect my Nginx in. But everything else works. How can you use Google to see if everything in the project is correct?
When I trigger the sync in the integration, I see the error 404 in the service account of my project in the HomeGraph API. Because no account is connected.
Same problem, after freaking freenom crippled free domains I bought domain at cloud flare. Created new project in google console, and now my phone does not connect to home assistant via google home. Anybody has solution? I tried “solution above” from user from Spain , and it doesn’t work
I switched to my own domain yesterday/today and as part of this tried to resetup this integration.
Im stuck with Could not reach [test] myapp like the posts above and none of the alternative solutions are yet to help.
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Hello,
I had the same problem and posted my solution here:
Your solution still does not work after all , I even made 4 times new project step by step according the manual from HA, and still no positive result. I had previously account working on another domain, but after freenom did its thing, I had to buy domain at cloudflare and since then I’m having this issue. Everything is fine until I enter credentials to link HA with google home, then I get message “Could not reach [test] Homeassistant. Please try again later” in googles case later means never!
I have tried even uninstalling google home, clearing cash, trying on some other browser… and I run out of ideas
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I am also stuck with exactly the same issue. I’ve set up google home link as described in the tutorial, but then the last step after logging into Home Assistant when I get sent back to Google Home app, I get the “Could not reach [test] myapp. Please try again” - none of the solutions in this thread helped so far 
Problem solved. “ Manual setup (if you don’t have Home Assistant Cloud)” Google Assistant without Nabu Cloud works.
My problem was Duckdns related to my internet provider.
The ip4 address is just a nat address. This causes Google to try to access my HA via the ip4 address. I could try my luck, but then there was no response from Google.
The solution was incredibly simple. The ip4 on Duckdns was deleted and an automatic update was prevented.
It’s been running for 2 days without any problems. But now I have 2 new ones  My VPN WireGuard® is causing problems. The IP4 is gone and will probably have to display it again for the Fritzbox. And on Google I get:
Add capabilities
Seamless Setup Support local query
not selected.
But I’ll find that too. It doesn’t work, it doesn’t exist.
This has to work. do you get your login? Check your proxy and Google answers you. My solution is below.
I get my HA login page, and there when I enter credentials I am getting message could not reach [test] homeasssistant. Please try again.
I even switched off rule in cloud flare, now I am getting following message
But that’s good. You just have to adjust your yaml config
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how to adjust?
its already there
google_assistant:
project_id: zoki-somethingsomething
service_account: !include SERVICE_ACCOUNT.JSON
report_state: true
expose_by_default: false
I have managed to connect, but only when I exposed all entities to google home, now is such clutter…
A switch would have been enough☺️
diagnosis update 2 : Solution
issue with ip and dns resolution
yes duck dns , no ip like other services can help you to get access over internet but if you using ipv6 only then your google home app show error "could not reach [test] all
solution you need ipv4 as well to resolve ipv4 if you don’t have ipv4 like me here is solution for that as well
buy domain or if you have domain configure with cloud flare it will resolve your ipv4 queries and transfer to you on you over tunnel
before you setup cloud flare make sure you turned of reverse proxy like nginx and duck dns or no ip or what ever you are using
setup Cloudflare in home assistant
then google home and Alexa will work without any error
I got this working after trying a few more times. It may have been a cloudflared issue for me.