If your Echo won't connect after entering the correct password, check if you're using a 5GHz-only network. Older Echo Dots are like that friend who still uses a flip phone they only understand 2.4GHz networks.
Connect your phone to the 2.4GHz one, then run the setup. You can merge them back later. Forget the Network: If youve changed your WiFi password recently, go into the Alexa app settings, find your device, and select "Change" next to the WiFi network name to update the credentials.
Best Tutorial on how to manually switch Wifi between 2.4 and 5GHz bands. Learn How to change from 2.4GHz to 5GHz Wireless Network Adapter in Windows 11/10/8/...

Plug in your Echo Dot. Go to the hotspot settings on your mobile device and note the hotspot name and password down. Do not enable the hotspot at this point. Open the Alexa app on your phone and click on Devices at the bottom.
Connect Phone and Echo to Main Network for Setup. Use Mobile Hotspot for Initial Setup. Connect Using Ethernet Adapter (Echo Models with Port).Echo cant see guest network. May be 5GHz network (most Echos need 2.4GHz).

Check If Your Network Adapter Supports 5GHz Wi-Fi. How to Connect to 5GHz Wi-Fi Windows 10. As the standards and speeds of Internet connection are constantly changed, lots of users are confused about all kinds of available options for wireless connectivity.