Google home could not reach error

after configuring google home using home assistant document and some you you tube video i always get “home could not reach [test] project name” after login
i get login screen in google home but after login it take a bit time and then error appear i try serval fix but nothing works i cross check all is ok and try multiple times but no luck always stuck after login screen

diagnosis update 1
make sure your duck DNS or what ever domain you use is perfectly configure not in home assistant but also on domain side as well
duck dns often update your ipv4 if you are using ipv6 make sure you check it first

while login in home app in phone make you are not connected to your local network

half way solve issue
still get same error “could not reach [test] project name” but get integration in home assistant it means i got connection

new error

Failed to call service button/press. Unable to sync devices with result code: 404, check log for more info.

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