I have set and reset my new chromecast 4 times now and eveytime I get all the way to the end and it tells me that my android and chromecast are not connected to the same wifi neteork. Again if reset it 4 times to the correct wifi and I get stuck on the same spot each time
I've restarted my phone, the router, the chromecast, the Google home, and my TV to no avail
All apps and platforms are up to date
It essentially says it can't see my device on this wifi network. Check that it's online and that your phone or tablet is connected to the same wifi network
Not sure if you still need info, but what nobody mentions is this. I connected my chromecast to the tv and the white light blinked consistently. I then searched wifi connections on my phone and connected to the chromecast which should be showing on the list of available wifis. Once connected it will say something about it being a poor connect or similar. Leave it connected anyway and then go to Google Home and connect on there. This will give you the opportunity to add in your new password for your new router. Then it all starts to set up correctly.
Hope that helps someone.